Habitat enhancement for rare butterflies on Fort Lewis prairies

Transcription

Habitat Enhancement for Rare Butterflies
on Fort Lewis Prairies
Cheryl Fimbel
The Nature Conservancy
March 2004
Goal : To restore and enhance components of native prairie systems
that are important to four rare butterfly species.
Executive Summary
The Fort Lewis Military Installation is important in a regional context because it contains the largest
remaining prairies in south Puget Sound and provides critical habitat for a number of rare and declining
prairie species. Among those declining species are four butterflies: the mardon skipper (Polites
mardon), Taylor’s checkerspot (Euphydryas editha taylori), zerene fritillary (Speyeria zerene
bremnerii), and the Puget blue (Icaricia icarioides blackmorei). The first two species, the skipper and
checkerspot, are candidates for federal listing under the Endangered Species Act. Within Fort Lewis,
they are currently restricted to a single locale, the Artillery Impact Area. The other two butterfly species
exhibit a more widespread distribution on Fort Lewis prairies.
The distribution and abundance of the four rare butterflies is influenced by habitat conditions, especially
the availability of larval and adult plant resources. The south Puget Sound prairie landscape has been
dramatically altered over the last 150 years due to changes in land use practices that accompanied
European settlement. Since that time, the prairies have been drastically reduced in size and fragmented,
and invasive plants have further altered the remaining prairies, with the result that the historical range of
landscape conditions is not available to present day prairie dependant species. In some areas, high
quality native plant communities appear to be largely restricted to the more drought-prone sites, leading
to a reduction in the diversity of habitat types available to butterflies in the prairie complex. Butterflies
typically use resources on the open prairies and in diverse microhabitats, depending on climatic
conditions. Access to a variety of habitats is likely to be especially important to adult and juvenile stage
survival and fitness during extremes in weather conditions. The degradation of native resources in
diverse microhabitats, especially moisture-retaining sites such as prairie edges and relatively mesic
areas, is a significant concern for butterflies. Habitat diversity is important because the distribution of
resources among a variety of sites can buffer the effects of unusual weather conditions on butterfly
populations, thereby promoting their long-term persistence in a dynamic environment.
The purpose of this document is to identify important habitat requirements of the four target butterfly
species, and propose strategies for habitat enhancements on the prairies that target those requirements.
This plan constitutes the next logical step in the conservation of prairies and their fauna, following on
the success of initial steps to control dense stands of Scotch broom (Cytisus scoparius), remove
invading conifers, and plant native grasses and forbs on Puget prairies. Proposed enhancement
strategies focus on three components of the prairies:
1. Vegetation Composition – Control of invasive species, especially Scotch broom and invasive
grasses, and planting of native grasses and forbs (especially larval and adult butterfly food
resources), have been, and will continue to be, the cornerstones to improving this component of the
prairies for butterflies. Control of exotic grasses poses the most formidable challenge to improving
the vegetation composition of the prairies for butterflies, as techniques for controlling these grasses
are less well studied, especially in a butterfly conservation context.
2. Habitat Structure – Targeting diverse structural/edaphic features of the prairies for enhancements,
in addition to open prairie sites, will promote habitat diversity. Diverse structural/edaphic features
to target include:
• Tree islands or edge habitats associated with oaks and conifers
• Sloping topography, especially low-lying swales
• Relatively mesic sites and prairie that grades into riparian zones.
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3. Process – Incorporating a ‘butterfly-sensitive’ fire regime that emphasizes a regular cycle of
burning on portions of the prairies, along with the creation of refugia within burned areas, should
promote the process component of the prairies and favor butterfly populations. Restoring fire as a
process on the prairies on a meaningful scale will be a challenge in the face of small, fragmented
prairies, unpredictable weather, burn restrictions, and encroaching development.
Three prairies in the Fort Lewis landscape were identified as high priority sites on which to enhance the
composition, structure and process of the prairie habitat (Figure 1). The selection was limited to three
prairies to concentrate resources into high quality habitat patches in three locales, rather than scattering
resources widely across multiple prairies, with fewer significant improvements. Concentrated resources
increase the chances that enhanced habitat patches will be located and used, and additionally, facilitate
mate location by the butterflies. The three high priority prairies, the Artillery Impact Area (AIA), the
13th Division Research Natural Area (RNA), and Johnson Prairie, were chosen based on their current
and historical use by rare butterflies, availability of native prairie vegetation, the presence of diverse
structural features, and compatible land uses. Within each of the three prairies, a network of three or
more habitat patches were identified for potential enhancements that emphasize improving habitat
elements identified as important to the rare butterflies. These habitat enhancement patches contain a
combination of open prairie habitat and proximal diverse structural features. Proposed enhancements
constitute an ambitious undertaking, and should be implemented slowly and with a strong research
component to avoid impacts to existing butterflies and their resources. It would also be prudent to adapt
existing management regimes to incorporate considerations for butterfly-sensitive management actions
outlined in the plan.
Two secondary priority prairies, the Weir Prairie complex and Training Area 7S, were identified as sites
to receive less intensive enhancement efforts (Figure 1). Strategies proposed for these sites are based on
a continuation of their existing management regime, and include maintenance of Scotch broom, woody
shrub and tree control efforts, with added emphasis on the prairie edges, and monitoring and treating
new invasives. A longer term strategy for these secondary priority prairies includes a higher level of
enhancement effort directed at non-native grass control, native species plantings, and incorporation of a
butterfly-sensitive fire plan, as recommended for the short-term on high priority prairies.
Monitoring and research programs that complement the proposed enhancement strategies would be
useful for improving those strategies and generally facilitate an adaptive management process. Several
research areas are reviewed in the plan:
1. Measuring success toward meeting habitat enhancement objectives proposed in the plan.
2. Evaluating the response of rare butterflies to habitat enhancements.
3. Monitoring the long-term population trends of rare butterflies in relation to the greater butterfly
community on Fort Lewis.
4. Gaining further understanding of a) the natural ecology of the rare butterflies and their
resources, and b) prairie enhancement techniques to promote improvements in habitat
management for rare species on Fort Lewis and the greater south Puget Sound region.
Evaluating the response of the mardon skipper and Taylor’s checkerspot to enhancement efforts is not
possible at Fort Lewis at this time due to their limited occurrence on a restricted access site (AIA). For
the purpose of gaining information on the value of select enhancement strategies proposed for these
species, an off-site research program warrants consideration. Cooperating with scientific partners on
local non-military lands outside of the Fort Lewis complex, where the target butterfly species occur,
would allow investigation into topics that relate directly to butterfly parameters, rather than their habitat.
In addition to the conservation of biodiversity, prairie enhancement activities will support the training
mission of the US army on Fort Lewis by removing dense stands of shrubs that hinder the movement of
troops over the landscape during training maneuvers. Furthermore, enhancement actions will only be
conducted at a time and place that does not conflict with military training activities.
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Figure 1. Map showing three high priority prairies, the Artillery Impact Area, Johnson Prairie, and the 13th
Division RNA, and two secondary priority prairies, Weir Prairie Complex and Training Areas 7S targeted for
habitat improvements on the Fort Lewis Military Installation.
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Table of Contents
Executive Summary
i
1. Introduction…………………………………………...……………...
1
2. Butterflies and the Importance of Habitat Diversity …………...…
2
3. Threats to Prairie Butterflies……………………………..…………
4
4. Important Habitat Considerations for Rare Butterflies ………….
4.1 Important Habitat Considerations by Species …….………………
4.1.1 Taylor’s Checkerspot …………………….…………..…..
4.1.2 Mardon Skipper ………………………….……..……….
4.1.3 Zerene Fritillary ………………………….…………..…
4.1.4 Puget Blue ……………………………….……….…….
4.2 Scotch Broom in Butterfly Habitat ………………….…………...
4.3 Summary of Important Habitat Considerations ……………..……
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7
7
10
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13
14
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5. Habitat Enhancement ……………………………………………..…
5.1 Where? - Spatial scales ……………………...……….….……….
5.1.1 Landscape Scale ……………………………….….…….
5.1.2 Prairie Scale ……………..……………….…….………
5.2 What? - Three components of the prairie …………....…………..
5.2.1 Vegetation Composition ………………..……………...…
5.2.2 Habitat Structure …………………….……….…………
5.2.3 Process …………………………..…………….………
5.3 How? - Enhancement Techniques ….……….………………...…
5.3.1 Controlling Woody Invasives.………………………..……
5.3.2 Controlling Herbaceous Invasives.……………………..….
5.3.3 Planting Native Species ……………………………...…..
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6. Habitat Enhancement Objectives …………..………..…………..… 34
7. Prairie Enhancement Strategies ………………..…………….……
7.1 Considerations for Implementing Management Actions …………..
7.2 Prairie Specific Enhancement Strategies ……...…………………
7.2.1 Artillery Impact Area ………………………….…...……
7.2.2 Johnson Prairie …………………………….…..………
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7.2.3 13th Division Prairie RNA ………………….….…………
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7.2.4 Weir Prairie Complex ………………………………… 51
7.2.5 Training Area 7S …………………………..……….… 51
8. Research and Monitoring to Guide Enhancement Actions ……….
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9. Timeline …………………………………….……..…………………
56
Acknowledgements ………………………………..……………………
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Personal Communications…………………………………….………..
57
Literature Cited ………………………………………………...………
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Butterfly Habitat Enhancement on Fort Lewis
1. Introduction
Native prairies of the south Puget Sound (hereafter condensed to ‘Puget’) constitute the most
endangered ecosystem in the state of Washington, and one of the most endangered ecosystems in the
United States (Altman 2003). The Fort Lewis Military Installation is important in a regional context
because it contains the largest remaining prairies in the Puget region, along with a significant
proportion of the region’s butterfly species (Morgenweck and Dunn 2003). Four species, the mardon
skipper (Polites mardon), Taylor’s checkerspot (Euphydryas editha taylori), zerene fritillary (Speyeria
zerene bremnerii), and the Puget blue (Icaricia icarioides blackmorei), have become increasingly rare
throughout their range in the Puget Trough - Willamette Valley ecoregion. Prairie habitat has
undergone extreme changes in the last two centuries, and consequently, the butterflies are reduced to
remnant populations on isolated prairies. All four species are proposed candidates for listing at the
state and/or federal level (see Table 1.1). Two species, the mardon skipper and the Taylor’s
checkerspot, both candidates for federal listing, were ranked by local experts as ‘very high’ in a
ranking of risks to the continued existence of the species (ENSR 2001, The Nature Conservancy 2002).
Table 1.1 Special status and priority rankings by local experts for the four target butterflies (ENSR, 2001, The
Nature Conservancy 2002).
Common Name
Scientific Name
Mardon skipper
Taylor’s checkerspot
Zerene fritillary
Puget blue
Polites mardon
Euphydryas editha taylori
Speyeria zerene bremnerii
Icaricia icarioides blackmorei
Federal listing
State
listing
Priority
Ranking
Candidate
Candidate
Species of concern
Endangered
Candidate
Candidate
Candidate
Very High
Very High
Medium
Medium
Within Fort Lewis, the mardon skipper and Taylor’s checkerspot are currently restricted to a single
locale, the Artillery Impact Area (AIA). In greater western Washington, these species have highly
restricted ranges in a limited number of other Puget prairies and ‘balds’. On a broader geographic
scale, the mardon skipper is known from 37 sites in four areas: 1) southern Puget Sound, 2) the Mt.
Adams area in southern Washington’s east Cascade Mountains, 3) the Cascade Mountains of southern
Oregon, and 4) Del Norte (north-coastal) California (The Xerces Society 2002b). The Taylor’s
checkerspot is believed extirpated from historical range in British Columbia, and restricted to a single
locale in Oregon’s Willamette Valley (The Xerces Society 2002a).
The other two species, zerene fritillary and Puget blue, received priority rankings of ‘medium’, and are
more widely distributed both on Fort Lewis and in other Puget prairies. This is especially true for the
Puget Blue, which is currently found on seven prairies on Fort Lewis (Morgenweck and Dunn 2003).
There is a population of zerene fritillaries on Johnson Prairie, and possibly some dispersing individuals
on the Weir and 13th Division prairies (Morgenweck and Dunn 2003). Outside of the south Puget
Sound region, zerene fritillaries occur on Vancouver, Gulf, and San Juan Islands (Pyle 2002), and a
handful of locations in the Willapa Hills. They are presumed extirpated from their range in the
Willamette Valley (Pyle 2002). Puget blue butterflies extend from Vancouver Island, south through
meadows of the Olympic Mountains, and into the greater Puget Trough region (Dunn and Fleckenstein
1997, Pyle 2002).
Conservation efforts that target these four candidate species are likely to improve conditions for other
prairie butterflies and organisms. Dunn and Fleckenstein (1997) conducted an analysis of the
distribution of the four candidate species, state monitor species, and the total number of butterfly
species in the Puget prairies. Their analysis suggested that prairies with candidate butterflies provided
habitat for a wide range of butterflies, not just the specific habitat needed by the rare species. Habitat
improvements that target the needs of the four candidate species, and that include the restoration of
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healthy prairies in general, should result in improvements for a wide range of native prairie-associated
butterflies and organisms beyond the target species of this document.
The purpose of this document is to summarize the scientific information concerning the habitat
requirements of the four target butterflies and propose strategies for habitat enhancements that target
prairie features likely to be important to these butterflies based on their requirements. Considerations
for a complementary research program are also provided. Management strategies are proposed
specifically for Fort Lewis, but the principles may be considered for wider application on Puget
prairies. The two federal candidate species received a greater emphasis in the plan due to their higher
priority rankings (Table 1.1). This program of enhancements constitutes the next logical step in the
conservation of Puget prairies and their fauna, following on the success of initial steps to control dense
stands of Scotch broom (Cytisus scoparius), remove invading conifers, and plant native prairie flora.
The goal of this enhancement program is described as follows:
Goal : To restore and enhance components of native prairie systems that are important to four
rare butterfly species.
If it is determined at a future date that butterfly populations will be augmented on Fort Lewis through
reintroductions, then a reintroduction or recovery plan should be developed that includes a welldocumented decision process for determinants of habitat suitability. The subject of the decision
process associated with reintroductions of the butterflies is not treated in this plan.
Finally, along with the conservation of biodiversity, prairie enhancement activities will support the
training mission of the US Army on Fort Lewis by clearing woody invasives that hinder movements of
troops across the landscape.
2. Butterflies and the Importance of Habitat Diversity
Most butterflies are not uniformly distributed throughout the landscape due to specific resource
requirements. Each species is uniquely adapted to a suite of environmental conditions derived from
intrinsic biological factors such as larval host specificity, low vagility, the need for close proximity of
individuals for mating behavior, and clumped distribution of nectar resources (Arnold 1980). Despite
the relatively specialist adaptations, some butterflies may change their use of host plants, habitats, or
microhabitats in different seasons or years (Mason 1997). Hays et al. (2000) report that nectaring by
Taylor’s checkerspots shifted to areas at the grassland/conifer edge during a dry period when flowers
on the open grassland had senesced, but fresh resources were available in the shade of the trees. They
also describe between-year differences in the nectar resources and characteristics of habitat used by
mardon skippers and zerene fritillaries in their Puget prairie study areas. The exact causes of these
shifts in resource and habitat use by butterflies were not always known, but the following rationales
were highlighted: variation in the availability of plant resources; responses to weather variables; and
responses to changes in the habitat by management actions such as Scotch broom removal (Hays et al.
2000).
The lifecycles of many butterflies incorporate different stages with diverse habitat requirements (New
1997). The varied requirements of different butterfly life stages with limited mobility means that
butterflies depend on access to diverse habitats offering a range of thermal microenvironments and
resources in close proximity (Weiss and Murphy 1990).
Two of the rarest butterfly species on Puget prairies require varying habitat conditions over the course
of their adult and larval development stages. The Taylor’s checkerspot and mardon skipper are among
the earliest butterflies to emerge as adults in early spring (Figure 2.1). These butterflies depend on early
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spring conditions that allow larvae, pupae, and adults to warm up enough to move, develop, and/or feed.
This is a challenge during the generally rainy and cool spring conditions on the Puget lowland prairies,
which can be made colder by the strong spring winds that increase on sunny afternoons when butterflies
would be most active.
Winter
Flight Periods
Stage
Taylor’s checkerspot
Larvae
Mardon skipper
Pupa
Puget blue
Larva
Zerene fritillary
Larva
Apr
May
Jun
Jul
Aug
Sep
Oct
Figure 2.1 Approximate flight periods and overwinter stages for rare butterflies in the Puget region
(flight times from Hinchcliff 1996 and Dunn and Fleckentstein 1997).
The rare early spring butterflies on Puget prairies require not only suitably warm conditions for growth
or emergence in the cool wet spring, but also larval host resources that remain pre-senescent during the
typically hot and dry northwest summers to support larval development. Summer larvae feed through
mid-summer to develop sufficiently to enter their over-wintering life stages (4th instar caterpillar for
Taylor’s checkerspot, and pupa for mardon skipper). Research on the Bay checkerspot (Euphydryas
editha bayensis) in California demonstrated the dependence of female reproductive success on the
relative timing of adult female emergence and hostplant senescence (Cushman et al. 1994).
Specifically, the larvae of eggs laid by early emerging females had the highest chance of surviving to
diapause before their food resources senesced, compared to the larvae of females that emerged later
(Cushman et al. 1994). The combination of conditions that favor early emergence of Taylor’s
checkerspot and other spring butterflies, while also allowing for mid-summer larval feeding may be
important on Puget prairies also.
Moderate weather conditions that favor all phases of growth and development allow population
numbers to increase. Unusual weather conditions such as an abnormally cold spring, or an early
summer drought, however, may disrupt the tight phase relationship between butterfly development and
resource availability (Weiss et al. 1987), leading to population declines. In times of unusual or
changing weather conditions, habitat diversity in the form of topographic or structural heterogeneity
becomes important, and may be key to the persistence of populations of insects that use small areas of
habitat (Ehrlich and Murphy 1987). Habitat heterogeneity has the potential to buffer a population
against the effects of environmental stochasticity (Hanski 2003), such as drought-induced senescence of
larval host plants, through differential survival of larvae in different micro-habitats. Prairies that are
structurally and compositionally diverse offer the best potential to meet the varying needs of the target
butterflies over the long-term.
Open portions of the prairies are extensively used by the four rare butterflies, yet diverse structural and
edaphic (pertaining to the soil or water environment) habitat features (hereafter condensed to ‘structural
features’) of the prairies may play important roles during times of climatic extremes or at critical times
of the year. Examples of diverse structural features that would be expected to enhance habitat diversity
on the prairies include:
• Prairie – woodland or forest edges
• Forest ‘nooks’ or pockets of prairie extending into the forest or woodland matrix
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•
•
•
•
Tree islands or individual trees on the open prairie
Low-lying swales
Prairie grading into riparian zones
Relatively mesic sites (i.e. sites that support prairie vegetation, but may retain moisture for
longer periods of time compared to drier prairie sites)
• Mounds, or deeper soil sites.
These diverse structural features create a variety of microhabitats for butterflies and their resources,
and other native fauna. They offer the potential for: protection from wind, escape cover, shading
effects, moisture retention, heat retention, and differences in humidity. These differences in
microclimate may be reflected in the plant species composition and their phenology, which further
enhances habitat heterogeneity.
In summary, the more diverse the habitat, the better the odds that the prairie complex can support the
variety of processes necessary to allow butterflies to complete their life stages in any given year, with
consequent population persistence. The buffering effects of heterogeneous habitats in the face of
unusual or extreme weather conditions may become more important if climate change is contributing to
local population declines (McLaughlin et al. 2002).
3. Threats to Prairie Butterflies
This plan is intended to guide the improvement of conditions for prairie butterflies on Fort Lewis
prairies, although it is important to note that the specific reasons for the declines of these rare species
are not completely understood. Extinctions and extirpations of butterflies, and biota in general, are
frequently attributed to environmental change, more specifically, some combination of habitat loss (due
to conversion or degradation), fragmentation, and alteration (Hanski 2003). Many insect populations
normally experience large fluctuations in size (Ehrlich 1992) as a result of weather, predation or disease.
These normal background fluctuations, coupled with habitat loss and alteration, can result in local
extirpations, with little chance of re-colonization due to the isolated nature of the habitat patches
(Hanski 2003).
Less well documented is the possibility that climate change poses a direct threat to butterflies, although
climate change-induced stresses have been cited as contributing factors in population declines or
extirpations, (USFWS 2000, Hanski 2003). Models of Bay checkerspot (Euphydryas editha bayensis)
population numbers and climate data show that changes in precipitation patterns associated with climate
change, can amplify background population fluctuations in these checkerspots, making them more prone
to local extirpations, especially in isolated populations (McLaughlin et al. 2002).
Finally, stochastic events acting on individual populations with no means for recovery due to isolation
(Ehrlich and Murphy 1987), and possibly loss of genetic diversity (Ehrlich 1992, Nieminen et al. 2001),
are additional factors that may contribute to population declines and extirpations. These various threats
may all be contributing to some degree to the declines of the target butterfly populations on Puget
prairies, although habitat modification stands out as the strongest potential contributing factor. This
section of the document will focus on the changes in the Puget prairie landscape as important threats to
the prairie obligate butterflies.
Smaller and Fragmented Prairies
The butterflies of the Puget Prairies evolved in a landscape that was very different than exists today. In
pre-European settlement times, the prairies were far more extensive, constituting the dominant
landscape feature of the Puget region (Crawford and Hall 1997). It is estimated that approximately 95%
of the historical extent of prairie and savanna habitat has been lost to urban, residential, and agricultural
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development, along with encroachment by Douglas-fir forest (Crawford and Hall 1997). The remaining
fragmented prairies are smaller and relatively isolated compared with their historical condition.
Invasive Species
The biological communities of these glacial outwash soils were strongly influenced by warmer and drier
climatic conditions than are in effect today (Crawford and Hall 1997). Since that time, climatic
conditions have become more conducive to forest cover, and the prairies have become a ‘plagioclimax’
community, requiring periodic disturbance to arrest succession and encroachment by conifers. A long
history of high frequency, low intensity, largely anthropogenic fires, combined with periodic summer
droughts and low soil fertility, served to maintain the fescue bunchgrass-dominated prairie community
over large expanses of suitable soil, despite the relatively wet climatic conditions that have prevailed in
recent history in western Washington (del Moral and Deardorff 1976).
Prior to European settlement in the mid-1800’s, the prairies of western Washington were burned
frequently, probably annually in many locales, by Native Americans (Morris 1934, Lang 1961, Norton
1979, Leopold and Boyd 1999). Cecilia Carpenter (1992) writes “… for as many years as they (our
Nisqually ancestors) could remember, during the fall of each year the vast prairie areas that lay on both
sides of the lower segment of the Nisqually River were burned.” A less frequent burning schedule,
approximately every 3 years, was used for prairie edges to encourage berry production and open the
understory (Purdue 1997, Leopold and Boyd 1999). Fires were frequently extensive in size, with early
visitors describing several miles of burned conditions (Lang 1961). Burning on the prairies and prairie
edges by Native Americans was drastically reduced with the influx of European settlers, eventually
leading to a policy of fire suppression. These same settlers also brought non-native pasture grasses for
their stock, and began the introduction of many invasive plants. The changes associated with European
settlement have resulted in a prairie landscape that is succeeding to conifer forest due to the absence of
periodic disturbance, such as fire, and native prairie bunchgrass communities that are being replaced by
invasive species. Thus, present day Puget prairies have been fragmented into smaller units, and the
remaining prairie lands have been altered through the encroachment and invasion of native and nonnative trees and shrubs.
Soils
Changes are also occurring below the soil surface. The soils of Puget Sound are characterized as
shallow, gravelly, well drained, low in fertility and productivity, and prone to drought (Lang 1961,
Crawford and Hall 1997). The nitrogen dynamics of these prairie soils are changing due to the addition
of N to the soil from:
a) N-fixing leguminous invasive plants such as Scotch broom (Haubensak and Parker, unpub
data).
b) Atmospheric deposition of N from the global N cycle (industrial and agricultural sources)
(Jeffries and Maron 1997). Atmospheric deposition of N constitutes approximately 25% of the
annual N load to the Puget Sound Basin (Inkpen and Embrey 1998).
Increases in available nitrogen can favor the establishment of aggressive non-native plants that are good
competitors for soil nutrients on enriched soils (Maron and Connors 1996), and crowd out native prairie
plants that evolved to compete on soils with relatively low nutrient levels. In this context of enriched
nitrogen soils, tall invasive grasses and conifers are becoming well established and often dominate
important butterfly habitats such as relatively mesic sites and prairie edge ecotones that otherwise would
have the potential to sustain butterfly larval food and nectar resources longer into the summer season.
Enriched soils that favor invasive plants increase the challenges to controlling these invasives and
restoring degraded prairie sites.
Loss of Habitat Diversity
Invasions of pest plants are especially evident on many of the more structurally diverse sites such as
relatively mesic areas and grassland - tree ecotones. These degraded structural features of the prairie
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present challenges for controlling invasives in a cost-effective manner. They are often difficult to
access with tractor mounted equipment, and are especially prone to re-invasion and establishment by
woody shrubs and trees due to proximal seed sources and less droughty conditions. This results in
lower habitat diversity values for the prairie complex as structurally diverse and sinuous prairie edges
and ecotones are converted to straight, solid edges by woody shrubs and trees, eliminating the mosaic
effects and ecotonal habitat gradients that are important to some invertebrates and other fauna. In
addition, prairie habitat adjacent to the edges is often further degraded by non-native pasture grasses
which form dense stands that crowd out the native grasses and forbs, further reducing the habitat
diversity values. Although tall non-native pasture grasses are becoming established throughout many of
the prairies, they are often especially abundant at the prairie – woodland edge, or on the deeper soils or
wetter sites (personal observation). This combination of factors has led to what appears to be a
disproportionate loss of high quality prairie edge and relatively mesic habitats. The result is that the
high quality, native-dominated plant communities on remaining prairies may be restricted to the more
drought-prone sites.
The degradation of these diverse structural features by invasive plants can seriously reduce the habitat
value for butterflies in those critical moisture-retaining sites, and by extension, the greater prairie habitat
complex during times of drought. This is especially true for univoltine butterflies (having one
generation per year, as opposed to multiple generations per year) such as the four rare species, which
require relatively long periods of time to complete their larval development, and depend on long-lasting
resources to complete a single lifecycle.
Loss of Oak Savanna and Woodland
Deciduous trees, such as the large Oregon white oaks (Quercus garryana) that made up the ‘oak
opening’, or oak savanna vegetation type described by surveyors for the Government Land Office in the
1850’s (GBA Forestry 2002) may have offered especially valuable habitat for the rare butterflies. They
allowed light penetration for early spring plant and larval development, while supplying summer shade
for persistence of host plants through the summer larval feeding period. The small and fragmented
prairies remaining today contain few solitary oaks or oak woodlands with native understory vegetation,
and gone are the expanses of oak savanna that were part of the prairie landscape. The loss of deciduous
trees with native understory on the prairies is one more factor contributing to the degradation of the
prairies, and possibly the decline of some of the rare butterflies.
Summary
The loss of some of the more productive habitats to invasive species often leaves largely the most
drought-prone soils as the remaining native prairie habitat. Present day prairies are a relatively
simplified version of a formerly complex prairie, savanna, riparian mosaic which likely contained
greater proportions of native prairie vegetation in different moisture gradients such as those found in
oak savannas, oak woodlands at the prairie margins, riparian areas, and relatively mesic sites, compared
to the range of conditions today.
The following constitute a summary of prairie characteristics that differ in today’s prairies compared
to historical conditions, and constitute potential threats to butterflies and other prairie obligate fauna.
1. Smaller, fragmented, and more isolated prairies.
2. Vegetation composition and prairie soil characteristics altered by woody and herbaceous
invasives.
3. Loss of landscape structure and habitat heterogeneity, with native bunchgrass communities
often restricted to the more drought-prone habitats.
4. Loss of the prairie process component – primarily a frequent, low-intensity fire regime.
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4. Important Habitat Considerations for Rare Butterflies
An excellent investigation conducted by Hays et al. (2000) at Scatter Creek Wildlife Area and Johnson
Prairie on Fort Lewis, quantitatively and qualitatively described habitat characteristics and nectar plant
preferences of the four target butterfly species. Results generated from this study are very useful in the
identification of habitat enhancements to promote habitat characteristics and nectar plants that should
benefit the four target butterfly species.
Despite the valuable information available for the rare butterflies’ nectar habitat characteristics,
empirically derived definitions of more subtle, or fine-grained habitat needs associated with juvenile life
stages are less well documented, as they are for most butterflies, due to time and money constraints on
long-term, detail-oriented, comprehensive research programs. The habitat requirements of all the life
stages of the target species play critical roles in the long-term survival of populations, and therefore are
important for management considerations such as habitat restoration and reserve design (Ehrlich and
Murphy 1987, Pullin 1996, Mason 1997). For example, characteristics of mate-finding habitat, sites
selected for oviposition, and habitat requirements for larval and pupal development of these rare
butterflies are less well understood, but would ideally be incorporated into habitat enhancements.
Natural history data are becoming increasingly harder to obtain, because the numbers of butterflies are
dwindling, and intact habitats have declined. Obtaining reliable data is further complicated by the
possibility that present day (and recent historic) populations of the target species may be occurring on
habitat patches that would be considered marginal in an evolutionary context, and therefore do not allow
the identification of the more subtle critical habitat needs for long-term persistence. This is likely true
where the prairies have experienced a disproportionate loss of some of the more structurally and
compositionally diverse habitat features compared with historical conditions, rendering those sites
unsuitable for the butterflies. As an extension of this concept, recent extirpations may have occurred on
habitat that historically acted as a population sink, and therefore does not represent a model for suitable
habitat conditions for the long-term survival of the species.
These caveats are introduced to highlight the limitations to identifying all habitat requirements of these
rare butterflies. In the interest of time, and the urgent need for management actions to improve
conditions for these rare species, habitat enhancement actions are best not delayed for the purpose of
detailed research (Ehrlich 1992). With the above qualifiers in mind, the best available information is
used to describe known or scientifically sound important components of habitat for the four target
species as a basis for enhancing those aspects of the habitat. Additional research is recommended to
occur concurrently with enhancement actions to address information needs (section 8).
4.1 Important Habitat Considerations by Species
4.1.1 Taylor’s Checkerspot
Research and observations of the Taylor’s checkerspot on Puget prairies have revealed information
useful in the identification of important habitat needs for this butterfly (Table 4.1 at the end of this subsection). Local quantitative studies on this species have been limited, however, by unfavorable weather
conditions and low population numbers (Hays et al 2000). The published literature contains information
from long-term and detailed investigations involving other checkerspot butterflies (Euphydryas spp),
which yield insights into some of the more subtle habitat requirements for these and other butterfly
species. Many of these research findings may have application on the Puget prairies.
Abundant nectar resources have been shown to be an important habitat element for checkerspot
butterflies in California, especially nectar availability late in the flight season (Murphy et al. 1983).
7
Abundant nectar can increase life span and egg production, both critical elements in the long-term
persistence of a butterfly population where larvae are often subject to high mortality rates (Singer 1972).
Research conducted on the Bay checkerspot (Euphydryas editha bayensis) reveals that a critical element
for this species is the availability of summer food resources for pre-diapause larvae (Singer 1972, Singer
and Ehrlich 1979). Many butterfly species deposit their eggs singly in the habitat, while female
checkerspots lay egg masses of 20 – 200 eggs (Cushman et al. 1994). Under favorable weather
conditions, starvation of larvae is minimized, and population numbers can dramatically increase. Under
conditions of extreme summer drought, the persistence of the population could depend on a few large
egg masses that were deposited on host plants located in habitat with greater moisture retention
capabilities compared with the more drought-prone open prairie sites. In this case, survival of eggs
from just a few egg masses could maintain the population at low levels, despite high background
mortality rates for eggs, larvae and pupae (Cushman et al. 1994).
In California, gopher mounds provided a microhabitat that supported checkerspot larval host resources
that grew larger and remained green for longer periods into the dry season compared to other open
grown resources (Singer 1972). Some Castilleja hispida plants (a larval host plant used by Taylor’s
checkerspots on the AIA) may be found on Fort Lewis prairies looking green and fresh, well after the
main population of Castilleja hispida has senesced. Whether due to growing on gopher or mole
mounds, or for other unknown reasons associated with the frequent fire regime or another factor, the
deferred senescence of just a few individual larval host plants that contain egg masses, could help to
explain the long-term persistence of Taylor’s checkerspots on the AIA where diverse microhabitats
associated with structural features of the prairie are limited. Gopher mounds may extend the availability
of butterfly resources on native-dominated prairies, but where non-native species are prevalent, these
same mounds may facilitate weed invasion. The community context is critical when evaluating or
managing for tunneling rodents.
Large numbers of Taylor’s checkerspots were observed using the relatively open habitat of the 13th
Division RNA prairie in the early 1990’s, and a small population continues to reside in the open
conditions in the southern region of the AIA. In addition to open prairie conditions, Taylor’s
checkerspots were found to use a variety of habitat types on the 13th Division prairie (Hays et al. 2000),
including:
• forest edges,
• wet meadows, and
• grasslands shaded by oak and Douglas-fir.
A Taylor’s checkerspot expert, Ann Potter (pers. comm.) has observed adult checkerspots flying in the
vicinity of coniferous trees when occurring in more open conditions, and Barry Bidwell (Morgenweck
2003) relates that he observed Taylor’s checkerspots gathering on the lee side of a tree or group of trees
to get out of the wind.
Ann Potter (pers. comm.) believes that trees have an important role to play in Taylor’s checkerspot
habitat. Most extant populations of Taylor’s checkerspot in Washington and Oregon (the Bald Hills and
the MacDonald Forest outside of Corvalis, Oregon), and recent extirpation (Glacial Heritage airstrip),
consist of relatively small or narrow patches of prairie enclosed by coniferous and deciduous trees
which probably serve to block the wind and contribute to a ‘parabolic’ type of heat reflectance or
retention. Ann Potter (pers. comm.) has also observed that Taylor’s checkerspots may be found at intact
balds in western Washington, but are not found at balds where the immediately surrounding trees had
been removed. The ultimate causes of these patterns are not known, but perhaps relate to: a) protection
from the wind, conferring warmer temperatures for larval rearing; and/or b) greater moisture retention at
tree edges, promoting prolonged flowering of nectar plants or greater vigor of larval host plants.
8
Taylor’s checkerspots in the Puget Sound region would be expected to benefit from heat capturing
south-facing slopes, prairie ‘pockets’, or other protected structural features on the prairies that provide
warm microhabitats due to their early spring larval feeding and adult emergence. The growth of postdiapause checkerspot larvae in early spring in California is influenced by local microclimatic conditions
that vary with slope, exposure, and time of year (Weiss et al. 1987). These checkerspot larvae are
described as ‘behavioral thermoregulators’, moving locations to raise body temperature and maximize
growth rates in the warmest microhabitats (Weiss et al. 1987).
It is likely that habitats lacking structural diversity, but containing abundant plant resources can support
Taylor’s checkerspots when weather conditions are favorable for the completion of their various life
stages. Access to resources in more diverse habitats probably becomes more important for both adults
and larvae in times of climatic stress (extremes in precipitation and temperature).
Available information argues for enhancing a combination of open sites and nearby structural features
on the prairie to provide a variety of microclimates, especially sites for early spring warming, combined
with moisture holding habitats to buffer the effects of drought on larval host plants in different
microhabitats during the summer.
Table 4.1 Larval and Nectar plant resources used by Taylor’s checkerspots on Puget prairies and in the greater
region (Hays et al. 2000, The Xerces Society 2002a).
Food Plants
Larval Plants
Harsh paintbrush (Castilleja hispida)
English plantain (Plantago lanceolata)
Sea blush (Plectritis congesta)
Comments
Non-native and abundant in many sites on Puget prairies.
Increasingly rare on Fort Lewis, restricted to one known
locale.
Nectar Plants
Common camas (Camassia quamash)
Nine-leaved lomatium (Lomatium triternatum)
Spring gold (Lomatium utriculatum)
Broadpetal Strawberry (Fragaria virginiana)
Puget balsamroot (Balsamorhiza deltoidea)
Important habitat considerations for Taylor’s checkerspots are as follow:
1. The presence of at least two species of larval food resources (Table 4.1) distributed on open
sites and nearby structurally diverse habitat features. In the event that one species senesces
under the prevailing conditions for that year, the alternate host might remain available to larvae.
Castilleja hispida, and Plantago lanceolata are the primary species to consider initially,
although Plectritis congesta could be considered following on the necessary research (see
section 8). Note that P. lanceolata is a non-native species that is abundant throughout our
Puget prairies and should not be planted.
2. The presence of abundant nectar plants distributed on open sites and nearby structurally diverse
habitat features (Table 4.1).
3. The presence of topographically/edaphically diverse sites, such as prairie pockets or forest
nooks and edges, mesic areas, and grasslands shaded by oak and Douglas-fir, in enhancement
areas for this species.
4. The presence of tunneling rodents (moles and gophers) that till the soil and provide sites for
establishment of native plants that may persist later in the season.
9
4.1.2 Mardon Skipper
Mardon skippers use Roemer’s fescue (Festuca roemeri) and red fescue (Festuca rubra - Cascades
populations) as larval host plants (The Xerces Society 2002b). Research into the silver spotted skipper
(Hesperia comma) in Britain (Thomas 1995) shows that although the foodplant, sheep’s fescue (Festuca
ovina) is common, females lay eggs only on plants that are adjacent to bare ground. Plants in crowded
conditions are ignored, perhaps due to physical obstruction or unfavorable microclimate. Interspersion
of bare ground among fescue may constitute an important habitat element for mardon skippers also.
Hays et al. (2000) describe observations of mardon flight behavior that emphasize the importance of the
short open profile of native bunchgrass communities. When mardon skippers were observed to
encounter patches of taller non-native grasses, they often flew quickly up and over these patches to
forage in another area dominated by native fescue (Hays et al. 2000). The short stature and open nature
of native bunchgrass prairies allows the adult butterfly to access both its oviposition sites in the fescue,
which are generally close to the ground, and an important nectar plant, the blue violet (Viola adunca)
(Potter et al. 1999, Hays et al. 2000).
Invasive plants, especially grasses such as colonial bentgrass (Agrostis capillaris) and the taller pasture
grasses fill the interstitial spaces among the fescue and crowd out important native nectar forbs, such as
Viola adunca. These invasive grasses not only compete with the native fescue, but block physical
access to oviposition sites at the base of the plant for the butterfly. Consequently, Hays et al. (2000)
highlight the importance of controlling invasive grasses in the native bunchgrass community for this
butterfly. Prescribed fire may constitute an important tool to promote the presence of bare ground and
short-stature vegetation characteristics that may be important for this species (see sections 5.2.3 and 7.1
for discussions of fire).
Over the course of two years, adult mardon skippers were observed foraging in high quality fescue
dominated habitat (Table 4.2), along a disturbed track/trail, an area of non-native graminoids at the edge
of and beneath a line of white oak trees, and a wet camas meadow at the Scatter Creek study area (Hays
et al. 2000). A mardon skipper expert, Jonathon Pelham (pers. comm.) relates that “often where you
find them depends on the weather conditions for that day or season”. These weak-flying skippers are
frequently associated with semi-drainages or low-lying swales that offer protection from wind or
slightly more mesic conditions for plants (Jonathon Pelham, pers. comm.). Mardon skipper adults
extensively used Festuca grassland along the edge of white oak stands at the Scatter Creek study area,
and during the windy weather, they were often only observed in these edge habitats, in the lee of trees
(Hays et al. 2000). Jonathon Pelham (pers. comm.) also relates that he has observed mardons using a
wide variety of ‘edge’ habitats, including road edges. The disturbed track/trail at the edge of the oak
stand at Scatter Creek contained a long patch of the introduced species Vicia sativa, which was
intensively used for nectaring by mardon skippers in 1999 (Hays et al. 2000). Some disturbed habitats
are characterized by low vegetation height (as in the trail or road bed itself , pers. obs.), which could
facilitate their use by mardon skippers.
Dense patches of Viola adunca were used heavily and ‘selected’ for nectaring by the mardon skipper at
Scatter Creek in 1998 (Table 4.3, Hays et al. 2000). An introduced plant species, Vicia sativa, became
available in 1999 following the removal of dense Scotch broom beneath a patch of oaks, and the flowers
were heavily used and ‘selected for’ by mardon skippers. The availability of flowers as nectar resources
varied considerably between years at this site, and Hays et al. (2000) propose that the “use of areas with
different species availability and phenology suggests that proximal diverse habitats may benefit the
mardon skipper”. In summary, it appears that the presence of short-statured native bunchgrass
communities in a variety of habitat types could benefit the long-term survival of this species.
10
Table 4.2 High nectar use prairie site characteristics (mean percentages) for mardon skippers at Scatter Creek
Wildlife Area, 1998 (Hays et al. 2000).
Roemer’s
Other Native
All Native
Non-native
Non- Native
Fescue
Grasses
Grasses
Grasses
Forbs
Native Forbs
Open Area
32%
2.2%
34%
15%
25%
10%
16%
Table 4.3 Mardon skipper nectar species and their characteristics at Scatter Creek Wildlife Area, 1998 and 1999
(Hays et al. 2000).
Nectar species
Early blue violet (Viola adunca)
Common vetch (Vicia sativa) (non-native)
Spring gold (Lomatium utriculatum)
Common camas (Camassia quamash)
Shephard’s purse (Teesdalia nudicaulis)
Western buttercup (Ranunculus occidentalis)
Density
11 plants/m2
0.2 – 0.5 plants/m2
0.4 plants/m2
0.0006 plants/m2
-
Nearest-Neighbor Spacing
0.2 m spacing in high use area
0.9 m spacing / 6-17m clumps
0.7 spacing
22.8 m
-
Important habitat considerations for mardon skippers are as follows:
1. The presence of abundant fescue interspersed with bare ground distributed on open sites and
nearby structurally diverse habitat features.
2. The presence of an abundant and diverse community of forbs for nectar distributed on open
sites and nearby structurally diverse habitat features, especially:
− Dense patches of early blue violet (Viola adunca)
− Common vetch (Vicia sativa) (non-native, do not plant)
− Spring gold (Lomatium utriculatum)
− Western buttercup (Ranunculus occidentalis)
3. The absence or low levels of invasive grasses.
4. The presence of structurally diverse habitats, including forest or disturbed edges, and relatively
mesic areas or swales in enhancement areas for this species.
5. Inclusion of a ‘butterfly-sensitive’ fire regime (see sections 5.2.3 and 7.1) as a habitat
enhancement tool to promote bare ground and short, open bunchgrass community.
4.1.3 Zerene Fritillary
Zerene fritillaries use violets as their larval host (Pyle 2002), and have been observed ovipositing on or
near Viola adunca on Puget prairies (Hays et al. 2000). Research on another zerene fritillary
subspecies, the Oregon silverspot (Speyeria zerene hippolyta) at Cascade Head in Oregon, revealed that
females oviposited in areas of higher violet density (> 20 plants/m2), that were characterized by lower
thatch depth (2.25 – 3.5 cm), and lower vegetation height (< 30 cm) compared with surrounding areas
(Pickering et al. 1992). Viola adunca are poor competitors (Bierzychudeck 2003) that are found on dry
sites and wet meadows (Pojar and Mackinnon 1994). Invasive species, including non-native grasses,
pose a problem for this low-growing forb by increasing thatch density and vegetation height, competing
for resources, and reducing open space for germination (Pickering 1997a, Pickering et al. 2000).
Experimental manipulations with Viola adunca show that fire stimulates seed germination (Pickering et
al. 2000, Bierzychudeck 2003). Violets respond well to burning in some instances, and fire is being
used as a management tool to enhance habitat for zerene fritillaries at Cascade Head (Pickering 1997a,
1997b). Fire would also be expected to produce favorable results for zerenes on Puget prairies by
stimulating violet germination, reducing thatch density and depth and vegetation height, and potentially,
the cover of some woody and grass invasives.
11
Zerene fritillaries are one of the later flying species on the prairies (Figure 2.1), and fly at a time when
there are relatively few prairie species flowering, especially during the latter half of their flight period.
Research on zerene fritillaries in the Puget prairies revealed that they nectared exclusively and ‘selected
for’ the non-native Canada thistle (Cirsium arvense) during a hot and dry year (Erigeron specious
senesced early), and then ‘selected for’ showy fleabane (Erigeron speciosus) the following year
characterized as cool and wet (Hays et al. 2000). Other nectar resources recorded for this species in the
Puget prairies include Solidago spathulata (perhaps actually Solidago missouriensis), Aster curtus (syn:
Sericocarpus rigidus), Chrysanthemum leucanthemum, Hypochaeris radicata, Senecio jacobaea,
Leontodon nudicaulis (Hays et al. 2000). Summer weather conditions largely determine which species
are available for nectar late in the summer, and thus, the availability of flowering resources varies
among years. An important consideration for zerene fritillaries is the availability of a variety of late
season nectar resources growing in a variety of structurally diverse habitats and ecotones, especially
moisture-retaining habitats, to assure that flowers are available somewhere in their habitat during the
typically warm and dry mid to late summer on Puget prairies. Furthermore, the presence of non-native
thistles in zerene habitat should not be discouraged unless the thistle population is threatening native
vegetation. It may be useful to investigate the potential for promoting late-flowering native thistles,
such as Cirsium undulatum, which has limited occurrence on Fort Lewis (LCTA 2003).
Zerene fritillaries are known to make use of open prairies, but are also associated with prairie edges and
ecotones (Morgenweck 2003, Morgenweck and Dunn 2003), and wooded nooks where adults “loaf,
nectar and court” (Pyle, 2002). The 1998 ‘high use’ nectaring area for zerene fritillaries in the Puget
prairie study was the most degraded area with the lowest cover of native grasses and forbs compared to
habitat used by the other three rare butterfly species studied by Hays et al. (2000) (Table 4.4). This is
not surprising, as they were nectaring on a species (Cirsium arvense) that is described for Fort Lewis as
‘common’ in poor quality prairie (dominated by non-native grasses), especially wet prairies (LCTA
2003). This species is a strong flier compared to the other rare butterfly species, and can range more
widely over the prairie, accessing different habitat types. The ‘entire’ areas used for nectaring in 1998
and 1999 exhibited higher quality prairie characteristics (higher cover values for native grasses and
forbs, and correspondingly lower values for non-native grasses and forbs, Table 4.4) (Hays et al. 2000).
Zerene fritillaries on Puget prairies do not appear to require native dominated grassland for nectaring
sites. They appear to require late season nectar sources, native or non-native, where access is not
hindered by woody shrubs. At the same time, zerenes require higher quality habitat that is suitable for
patches of Viola adunca, characterized by low vegetation height and low thatch depth (Pickering et al.
2000). This combination of requirements would argue for enhancement of a combination of open
prairie, prairie edge, and moisture-retaining habitats on the prairies to promote violets and nectar
resources listed in Table 4.5 and other late-season forbs.
Table 4.4 ‘High Nectar Use’ and ‘Entire Sample Area’ (bold font) prairie site characteristics (mean percentages)
for zerene fritillaries at Scatter Creek Wildlife Area, 1998 and 1999 (Hays et al. 2000).
Roemer’s
Other Native
All Native
Non-native
Non- Native
Native Forbs
Open Area
Fescue
Grasses
Grasses
Grasses
Forbs
0%
5 – 11%
15%
4 – 12%
15%
16 – 23%
51%
16 – 27%
12
9%
10 – 15%
17%
7 – 15%
7%
24 – 45%
Table 4.5. Zerene fritillary nectar species and their characteristics at Scatter Creek Wildlife Area, 1998 and 1999
(Hays et al. 2000).
Nectar species
Density
Spacing
2
Canada thistle (Cirsium arvense) (non-native)
3.5 plants/m
0.3 m spacing in high use
Showy fleabane (Erigeron speciosus)
0.002 plants/m2
13.4 m spacing
Spikelike goldenrod (Solidago spathulata)*
0.001 plants/m2
16.5 m spacing
*Hays et al. (2000) list spikelike goldenrod as a nectar source, but on Fort Lewis prairies, this species is rare and
flowers around June, and would not likely be available as a nectar source. Missouri goldenrod (Solidago
missouriensis) is more common and tends to bloom later in the season (LCTA 2003, Rod Gilbert, pers. comm.),
and therefore would more likely be available during the zerene fritillary flight season. For this reason, #2 below,
and enhancement plantings proposed for zerene fritillaries (Table 5.3), include Solidago missouriensis rather than
Solidago spathulata.
Important habitat considerations for zerene fritillaries are as follows:
1. The presence of patches of dense concentrations of violets (Viola adunca >20 plants/m2) in
habitat characterized by:
− low thatch depth (2.25 – 3.5 cm), and
− low vegetation height (< 30 cm).
2. The presence of an abundant and diverse community of late season forbs for nectar
distributed in open sites and nearby structurally diverse features, especially:
− Showy fleabane (Erigeron speciosus)
− Canada thistle (Cirsium arvense) (non-native, do not plant)
− Native thistles, (e.g. Cirsium undulatum)
− Missouri goldenrod (Solidago missouriensis)
− White-top aster (Sericocarpus rigidus).
3. The inclusion of structurally diverse habitats, including mesic areas, forest nooks/prairie
pockets, swales, tree islands, and prairie edge components in enhancement areas for this
species.
4. Inclusion of a ‘butterfly-sensitive’ fire regime (see sections 5.2.3 and 7.1) as a habitat
enhancement tool to promote violets and associated desirable habitat characteristics.
4.1.4 Puget Blue
Puget blue butterflies are known to use sickle-keeled lupine (Lupinus albicaulis) for mating,
ovipositing, larval feeding, and nectaring (Hays et al. 2000). These butterflies are “completely
dependant upon lupines”(Pyle 2002). Puget blues are highly associated with L. albicaulis on Fort Lewis
and other Puget prairies, and high use site characteristics reflect relatively high quality prairie conditions
(Table 4.6). The anomaly is Training Area 7S, where they are known from the recent past, but were not
detected during the 2003 butterfly surveys (Morgenweck and Dunn 2003), despite an abundance of L.
albicaulis and other forbs at this prairie. Lupinus albicaulis is an early successional species that relies
on disturbance factors such as fire to persist (Guppy and Shepard 2001), and thus prescribed burns
would likely be helpful in promoting this plant species.
A variety of plant species were used for nectaring by Puget blues in the 1998 and 1999 years of the
Hays et al. (2000) study (Table 4.7), although there was a clear preference both years for feeding from
unopened flowers of L. albicaulis. Although the exact feeding mechanism on these unopened flowers is
not known, there may be an association between aphids and L.albicaulis flowers, where the aphids
produce honeydew that is attractive to butterflies (Morgenweck 2003). This topic should receive further
attention to better understand the relationship between Puget blues and this important resource. Hays et
al. (2000) also observed ants ‘tending’ and defending Puget blue larvae. Ant – butterfly associations are
known from other Lycaenid species (Pyle 2002), and further details of the relationship between ants and
13
Puget blues would be helpful for understanding habitat needs and improving enhancement actions (see
section 8 for further research).
Table 4.6 High nectar use prairie site characteristics (mean percentages) for Puget blues at Johnson Prairie,
1998 (Hays et al. 2000).
Roemer’s
Other Native
All Native
Non-native
Non- Native
Fescue
Grasses
Grasses
Grasses
Forbs
Native Forbs
Open Area
16%
4%
20%
15%
42%
19%
3%
Table 4.7 Puget blue nectar species and their characteristics at Scatter Creek Wildlife Area and Johnson Prairie,
1998, 1999 (Hays et al. 2000).
Nectar species
Sickle-keeled lupine (Lupinus albicaulis)
Common vetch (Vicia sativa) (non-native)
Oregon sunshine (Eriophyllum lanatum)
Manroot (Marah oreganus)
Graceful cinquefoil (Potentilla gracilis)
Density
0.05 - 1.8 plants/m2
0.001 - 14.1 plants/m2
0.002 – 0.03 plants/m2
1.6 - 12 plants/m2
0.0005 plants/m2
0.09 - 0.2 plants/m2
Spacing
0.5 – 1.9 m spacing
0.1 – 0.4 spacing
24.6 m spacing
Important habitat considerations for Puget blues are as follows:
1. The presence of dense concentrations of Lupinus albicaulis for larval feeding and adult
nectaring.
2. The presence of an abundant and diverse community of forbs for nectar (Table 4.7)
3. The inclusion of a ‘butterfly-sensitive’ fire regime (see sections 5.2.3 and 7.1) as a habitat
enhancement tool to promote lupines and other forbs.
4.2 Scotch Broom in Butterfly Habitat
Scotch broom is a non-native invasive plant that degrades butterfly habitat on the Puget prairies. Hays
et al. (2000) summarize their data on Scotch broom cover and height with the following generalizations:
1. Scotch broom cover was below 20% in all sample areas in habitat used by butterflies in the
study.
2. Areas with higher butterfly densities generally had lower coverage of Scotch broom.
3. The density, coverage, and height of Scotch broom were less in high use areas than in entire
sample areas.
Furthermore, mardon skippers and Puget blue butterflies avoided (no or low use relative to abundance in
the habitat) Scotch broom flowers as a nectar resource in their habitat.
4.3 Summary of Important Habitat Considerations
This section synthesizes important habitat considerations for the rare species butterfly community, or
subsets of this community, identified through the butterfly habitat research conducted by Hays et al.
(2000), the published literature, and local experts. This summary emphasizes hostplant and nectar
resources as important habitat elements because butterfly population size has been shown to be strongly
associated with resource availability (Schultz and Dlugosch 1999).
14
A summary of important habitat considerations for the rare butterfly community includes the
following:
1. The absence or low height and cover of Scotch broom and other woody invasives on prairies
and their structurally diverse habitat features.
2. The absence or low cover of non-native invasive grasses in important butterfly habitats on
prairies and their structurally diverse habitat features.
3. The presence of diverse native prairie vegetation communities on prairies and their
structurally diverse habitat features.
4. The presence of a diversity and abundance of forbs in different prairie habitat types that
flower at different times throughout the season, with particular attention to late season nectar
resources (including non-native species) which are limited on Puget prairies.
5. The presence of dense concentrations of larval host plants for the target butterflies, including
Castilleja hispida, Lupinus albicaulis, and/or Viola adunca, in high quality prairie
interspersed with Festuca roemeri and some bare ground in different prairie habitat types.
6. The implementation of a ‘butterfly-sensitive’ fire regime (see section 5.2.3) to promote
prairie habitat characteristics that benefit rare butterflies.
7. The implementation of management activities conducted “a) with knowledge of rare
butterfly locations and habitat (resource) use, and b) at a scale that will not adversely affect
rare butterfly populations” (Hays et al. 2000).
5. Habitat Enhancement Strategies
Section 4 above highlights important habitat considerations for the four rare butterfly species on Puget
prairies. This section describes proposed strategies for translating important habitat considerations into
enhancement actions, including where, what, and how to enhance.
5.1 Where? - Spatial scales
Enhancement strategies were developed to guide enhancement actions across the Fort Lewis landscape,
and within individual prairies. The strategies for these two spatial scales are elaborated below.
5.1.1 Landscape Scale
The majority of the enhancement actions recommended in this plan focus on three high priority prairies
(Figure 1). The rationale for this approach is to concentrate resources into high quality habitat patches
on a few prairies, rather than scattering resources widely across multiple sites with fewer significant
improvements. Concentrated resources increase the chances that these resources will be located by
adult butterflies, and consequently, facilitate mate location, and at the same time minimize larval
dispersal out of a resource patch. Historically, the three high prioritie prairies have displayed the
highest butterfly diversity on Fort Lewis (Morganweck 2003). The selection of prairies as high priority
for enhancement was based primarily on the current and recent historical presence of rare butterflies,
with consideration of additional criteria outlined in Table 5.1.
15
Table 5.1. Criteria for choosing high priority and secondary priority prairies for butterfly enhancements.
T=Taylor’s checkerspot, M=mardon skipper, Z=zerene fritillary, P=Puget blue and +=above average, compared
with these and other prairies.
Decision Criteria
AIA
Johnson
13th RNA
Weir
TA7S
Current use by butterflies
T, M, P
Z, P
P
P
Historical use by butterflies
T
T, Z
T, P
Diverse structural features and microsites
+
+
+
Compatible land use, RNA’s & Seibert areas.
+
+
+
+
Native prairie vegetation
+
+
+
+
+
Potential to support metapopulation dynamics
+
+
+
High Priority Prairies
•
Artillery Impact Area
Currently supports the only known populations of Taylor’s checkerspots and
mardon skippers on Fort Lewis. Also supports a population of Puget blue
butterflies. Contains a diverse and abundant fire-maintained native forb
community, including a population of Castilleja hispida.
•
Johnson Prairie
Historically supported a population of Taylor’s checkerspots, and currently
supports the most diverse and abundant butterfly population on Fort Lewis,
including zerene fritillaries and Puget blues. Also contains an abundant and
diverse native forb community, including a population of Castilleja hispida.
Contains diverse structural features including swales, tree islands, and oak
woodlands.
•
13th Division RNA
Currently supports a population of Puget blue butterflies. Historically
supported a large population of Taylor’s checkerspots, a population of
zerene fritillaries, and a relatively diverse butterfly community. Currently
contains some high quality native prairie vegetation along with important
structural features, especially riparian habitat. Protected by RNA status and
Seibert stakes.
In addition to the high priority sites, two secondary priority prairies (Figure 1) are recommended to
receive less intensive enhancement actions such as a) woody vegetation control and b) monitoring and
treating new invasive species, on open grasslands, adjoining oak woodlands, and prairie edges. A longterm strategy could include increased enhancement efforts on these two prairies, including greater
control of invasive species (especially grasses), and enhancement plantings, as recommended for the
high priority prairies, to increase the overall potential for long-term persistence of the four target taxa.
This will be especially important for the Weir Prairie Complex, which, together with nearby Johnson
Prairie, could form a potentially larger network of high quality prairies to support metapopulation
dynamics.
Secondary Priority Prairies
•
Weir Prairie Complex
The lower and upper Weir prairies, together with South Weir, support a
population of Puget blues. This prairie complex contains abundant native
fescue bunchgrass, although the abundance and diversity of native forbs on
these prairies are relatively limited compared with the other prairies
mentioned previously. Diverse structural features are also relatively limited,
although upper Weir prairie contains considerable sections of oak
woodlands, and the southern portion has a large swale. The Weir prairies
are afforded limited protected by RNA status, and Weir prairie south of
16
Rainier Road (South Weir) constitutes the northern extension of a potential
conservation area adjacent to Fort Lewis.
•
Training Area 7S
Historically supported a population of Taylor’s checkerspot. Recently
supported a population of Puget blues. Contains a relatively abundant and
diverse native forb community, including a population of Castilleja hispida,
and diverse structural features such as forest edges, oak woodlands, and
terraces. Large portions of this prairie have been converted to a gravel pit.
A portion is protected by Seibert stakes.
5.1.2 Prairie Scale
For each of the three high priority prairies mentioned above, improvements for butterflies would be
served by enhancing three components of prairie habitat: a) vegetation composition, b) habitat structure,
and c) process. Each of these three components will be treated in further detail in section 5.2.
Enhancements are not likely to be distributed continuously across each prairie due to constraints in
financial, labor, and plant propagation resources. Instead, a strategy is proposed that concentrates
enhancements, and especially outplantings of butterfly plants, into a network of three or more habitat
enhancement patches, each a minimum of 2 ha in size (see ‘Patch Size’ below), in each prairie. These
habitat enhancement patches would ideally contain one or more patches of concentrated plant resources
for butterflies (butterfly resource patches) as conditions allow (i.e. where appropriate, according to
butterfly and plant species-specific requirements). Thus, butterfly resource patches (separated by < 50
m) combine to make up a habitat enhancement patch that is at least two ha in size. Prairie wide, it
would be best if the three or more, 2+ ha size habitat enhancement patches were separated by no more
than 200 m (see ‘Distance Between Habitat Patches’ below, and section 5.3.3 for further discussion)
where possible, eventually closing the gap to 100 m in future phases of butterfly enhancement planning.
The exception is the Artillery Impact Area, where the potential to undertake management activities is
limited due to restricted access and safety concerns. This prairie site is perhaps the most important due
to the presence of mardon skippers and Taylor’s checkerspots, and therefore warrants special efforts to
include enhancements compatible with the site’s limitations (see section 7.2.1).
Patch Size
Ideally, enhanced habitat patches should be large and closely spaced, although limited resources
constrain the actualization of this model. Alternatively, the optimal size and arrangement of enhanced
butterfly habitat patches should be based on knowledge of the dispersal characteristics and population
demographics of the target butterfly species. Unfortunately, data for these parameters are lacking for
the four rare butterfly species. In this case, inferences may be drawn from the treatment of these
questions for other butterflies.
Crone and Schultz (2003) treat the question of minimum patch size for the persistence of populations of
the Fender’s blue butterfly (Icaricia icarioides fenderi). Using computer models that incorporated field
data for this species, they determined that minimum patch sizes of 2 – 6 ha for isolated patches were
necessary for the long-term persistence of this butterfly, depending on the variability of the population
growth rates. Baguette et al. (2000) determined that habitat patches ~ 1 ha in size yielded less
emigration and immigration than smaller patches (0.3 – 0.6 ha) for three butterfly species (two Pierids
and one Lycaenid in Belgium). In the absence of specific data derived directly from our target species,
it appears reasonable to incorporate information from these butterflies, and start with patches that are
approximately 2 ha in size, as three of our four butterflies are relatively small and use dense patches of
resources, and are relatively weak fliers. Each of the three high priority prairies on Fort Lewis is large
enough to accommodate a network of patches of this size. The value of these habitat patches to the
17
butterflies is increased where they are incorporated in a network and spaced within potential dispersal
distance, as opposed to being isolated patches.
Distance Between Habitat Patches
The distance between enhanced habitat patches on the prairie should be no greater than the dispersal
capabilities of the target butterfly species to allow movements among patches. Long distance
movements for mardon skippers are estimated at 400 m (Runquist 2003). Research on the Bay
checkerspot in California reveals that directed dispersal is not likely beyond 50 m, although individuals
are capable of travel up to 5.6 km in less than 24 hours over flat open terrain (Harrison 1989). Arnold’s
(1980) research on six Lycaenid butterfly species revealed that adult movements of these relatively
weak fliers averaged less than 37 m, yet some adults dispersed 100 – 200 m to peripheral patches of
their foodplant in adjacent grassland. Schultz (1998) describes a mark-recapture study where a limited
number of Fender’s blue butterflies dispersed between habitat patches separated by 150 m. The
Taylor’s checkerspot, mardon skipper, and Puget blue butterflies are all considered to be weak fliers,
and consequently, relatively poor dispersers (Char and Boersma 1995). In the absence of dispersal
distance data for the four butterfly species on Puget prairies, a rule of thumb could be to space habitat
patches at intervals of < 200 m, and closer to 100 m where possible (Ann Potter, pers. comm.), with
relatively open prairie habitat (non-forest) stretching between patches, to facilitate movement among the
different habitat patches within a prairie.
5.2 What? - Three components of the prairie
An earlier discussion (section 3) described primary threats to Puget prairies and their butterflies. Based
on the threats identified in that section, three components of the prairies will be targeted to ameliorate
those threats, and enhance conditions for prairie butterflies:
1. Vegetation Composition
2. Habitat Structure, and
3. Process.
5.2.1 Vegetation Composition
Control of invasive species and planting of native grasses and forbs, especially larval and adult food
resources, have been and will continue to be the cornerstones to improving the vegetation composition
of the prairies for butterflies. Scotch broom removal has been a primary activity on the Fort Lewis
prairies to date, and this important activity will continue to form the foundation of prairie restoration
efforts, upon which more specific butterfly enhancements can build. Enhancements proposed to
improve vegetation composition are based on the following considerations:
• High quality prairie vegetation composition parameters (cover estimates by plant category) for
the butterfly community could serve as baseline targets for general butterfly enhancement
actions (Table 5.2).
• Butterfly species-specific resource targets (section 6) could be considered for habitat
enhancement patches where enhancement actions target a specific butterfly species.
• Enhancements that emphasize augmentation of known larval host plants for the rare species,
and close interspersion of nectar plants among the larval hosts, are likely to considerably
improve butterfly habitat (Schultz and Dugosh 1999).
• In some cases, enhancement plantings could include not only important butterfly resources, but
also the more common species that characterize high quality native vegetation on the prairies
and in the oak woodland - savanna understory to promote a healthy and functional prairie. See
tables 5.4 and 5.5 in section 5.3.3 for lists of species that characterize these two communities.
18
Table 5.2. High quality habitat characteristics synthesized from high quality habitat conditions described by
Hays et al. (2000) for areas used by butterflies on Puget prairies, and Dorner’s (1999) research on prairie
quality on Fort Lewis.
Plant Category
Characteristic
Scotch broom
Native grasses, dominated by fescue
Native forbs
Non-native grasses and forbs
< 6% cover, and < 0.26 m in height
> 35% - 60% cover
> 25% cover
< 35% cover
To improve the vegetation composition for specific butterflies, a first approach would be to expand
existing high quality resource patches for the four butterfly species in each of the three high priority
praires. Secondarily, establishing butterfly resource patches in close proximity (< 50 m) to the existing
resource patches would improve habitat. At the same time, habitat enhancement patches (section 5.1.2)
identified for the three high priority prairies (section 7) could receive enhancements and plantings to
create one or more butterfly resource patches within the habitat enhancement patch.
5.2.2 Habitat Structure
Diverse structural features of the prairies should be targeted for enhancements in addition to open
prairie sites to promote habitat diversity. Controlling invasives, and increasing the native plant
composition of structural features described below will increase the diversity of habitat types and
microsites available to the butterflies, and the ecological community as a whole.
Diverse structural features to target include:
• Tree islands and edge habitats, especially oak woodlands, and prairie pockets that extend into
the forest or woodland matrix
• Sloping topography, especially low-lying swales
• Riparian zones and relatively mesic sites.
5.2.3 Process
Fire
Fire played an important role in the history of Puget prairies. Prior to European settlement in western
Washington, fires were frequent, relatively low in intensity, and burned extensive areas of the prairie
landscape, including prairie edges and adjacent woodlands and forest (Morris 1934, Lang 1961, Norton
1979, Leopold and Boyd 1999). The regularity of these fires (annual burning on Nisqually prairies
[Carpenter 1992]) was an important process that favored prairie vegetation and helped to arrest forest
succession on the prairies (Boyd 1999). Fire suppression is the current policy in the region, although
prescribed burns conducted by Fort Lewis personnel are implemented on portions of the prairies during
the summer or fall. Tveten and Fonda (1999) examined the effects of the military’s prescribed burning
program, and found that both frequent burning, and the absence of burning, favored different suites of
non-native species over native grasses and forbs in prairies and oak woodlands. The authors concluded
that, compared with ‘frequent burning’, and ‘no burning’ fire regimes, “fire intervals shorter or longer
than the 3 – 5 year fire rotation now employed on Fort Lewis are detrimental to fescue prairie and oak
woodland.” It is important to note that this observation should be considered in a general sense, as the
authors did not conduct controlled experiments to specifically test different fire return intervals. It is
reasonable, however, to consider that frequent burning and no-burning fire regimes would be deleterious
to prairie habitat, while a regime of repeat burning at some moderate interval could be beneficial.
Fire has numerous effects on the physical, chemical and biotic components of grasslands that influence
the functioning of prairie systems in general, and butterfly habitat in particular. Specifically, fire has the
potential to impact the following positive and negative attributes of the prairie soil and vegetation
community:
19
•
•
Reduce moss and thatch layers.
Increase the bare ground component of the prairies, which:
− allows butterfly access to the base of plants for oviposition,
− creates nesting sites for ground nesting invertebrates such as bees (e.g. bumblebees
pollinate Castilleja spp.)
− provides germination sites for native plants and non-natives – depending on context.
• Reduce woody shrub cover (Clark and Wilson 2001).
• Increase the availability of nitrogen in the immediate pre-burn phase, which favors nonnative grasses (Wan et al. 2001)
• Over time, reduce the total nitrogen pool, thereby favoring native plants (probably requires
repeat burns, Wan et al. 2001).
• Reduce the cover of some invasive grasses (Grace et al. 2001) and native perennial grasses
(Corbin et al. in review)
• Enhance forb germination and abundance (Schuller 1997, Maret and Wilson 2000).
• Promote short-stature prairie vegetation (through the combination of reducing grass cover
[Tveten and Fonda 1999], and nitrogen levels).
The impacts of a prescribed burn on the vegetation community would depend on the context, including
the fire’s characteristics and the existing pre-burn vegetation. Where pre-burn vegetation is dominated
by native species, fire would be expected to have little negative effect on the vegetation. Where preburn vegetation includes an abundance of non-native plants and their propagules, fire has the potential
to increase non-native vegetation.
At the same time, fire would be expected to result in some mortality of butterflies, and therefore
requires careful consideration when used in habitat containing isolated populations of rare butterflies.
An analysis by Schultz and Crone (1998) examined the tradeoffs of short-term negative effects vs. longterm positive effects of fire on a population of Fender’s blue butterflies (Icaricia icarioides fenderi) in
the Willamette Valley of Oregon. Their work revealed that the theoretically best fire strategy was to
burn one-third of the habitat every year or two. This would result in a fire return interval of
approximately every three to six years. A review of research related to prescribed burns and prairie
insects highlights the value of a mosaic of burn stages in promoting insect diversity, and the importance
of patchy burn patterns that promote an interspersion of burned and unburned habitat for rapid recolonization of burned sites (Reed 1997). It is likely that the judicious use of fire to create a mosaic of
burned and unburned patches would be beneficial for enhanced butterfly habitat in the context of Puget
prairies also.
It is not possible, nor is it necessarily desirable, to duplicate the historic fire regime in the current
context of small populations of rare butterflies distributed among isolated and fragmented prairies with
increased fuel loads. At the same time, fire is an important process and tool for maintenance of a
diverse prairie landscape, and enhancement efforts for butterflies would benefit from further
investigations into strategies to maximize habitat improvements through the use of fire, while
minimizing potentially harmful impacts. The development and implementation of a ‘butterfly-sensitive’
fire regime that incorporates a strong research component may provide the best approach to evaluating
the tradeoff in the costs and benefits to butterflies and their habitat. The ‘butterfly-sensitive’ fire plans
should be designed in the very near future for each high priority prairie (other than the AIA), followed
by the second priority prairies. These plans should be designed through collaboration among partners
that include fire, butterfly, and community ecology experts (see section 7.1 for elaboration of
considerations for a ‘butterfly-sensitive’ fire regime).
Wildlife
Pocket gophers (Thomomys mazama) historically contributed to the prairie process component. Their
tilling and mound forming habits influence plant germination and phenology dynamics. Their
20
herbivorous diet consists of roots, bulbs, and tubers, along with the above ground portions of plants,
which could serve to locally thin out prairie plants. Large native ungulates such as elk (Cervus elaphus)
also may have played a greater role historically in the prairie and prairie-ecotone processes than they do
today. Elk can form large herds, and they probably had seasonal influences on prairie processes in
specific locales through their grazing and trampling actions. In the current context of widespread nonnative weeds, the soil disturbing processes of tunneling rodents and large ungulates could have negative
effects on native prairie communities by facilitating weed invasion. Given the lack of definitive
information to guide the incorporation of these faunal elements in the prairie process component, this
plan will not provide further treatment of these topics. It would be useful to explore these topics
however, through future research (section 8).
Native Americans
Local Native American tribes gathered much of their dietary carbohydrates and vegetable protein, along
with medicines, from the Puget prairies (Lombardi 1997). Their gathering activities included primarily:
a) the use of digging sticks to till and aerate the soil and dig out camas bulbs, and b) thinning of plants
(Norton 1979). Regular use of the prairies in this way by native peoples would have had an effect on
the soil and vegetation of the prairies, and could be considered another process that was influential in
shaping the historical condition of the prairies. The extent and effects of digging and thinning activities,
and their implications in the present context of invasive species, are not well described, and therefore
will not be treated further in the plan, but constitute good subjects for further investigation (section 8).
European Settlers
Settling of the prairies by Europeans resulted in the direct loss of habitat through development and the
indirect loss through cessation of frequent burning (see Fire above). The condition of the prairies were
further altered by changes in land use such as cultivation for agriculture, heavy grazing by livestock, and
cutting oak for firewood. These processes permanently altered the composition and structure of the
native vegetation and soils. Although rural settlement processes have contributed to the degradation of
the greater prairie landscape over the years, they are no longer operating on Fort Lewis prairies, and will
not be addressed further in this document.
Current Use
Current processes operating on Fort Lewis prairies include recreational activities, military training,
natural resource management activities, and protection via designated research and natural areas.
Civilians frequently use Fort Lewis prairies for recreational purposes such as horseback riding, dog
training, model airplane flying, pheasant hunting, occasional large events, and unauthorized
motorcycle/ORV use. While most of these activities have limited impacts on the prairies, horseback
riding can degrade native habitat by introducing non-native pasture grasses through their feed hay and
manure. Recreational vehicle traffic disturbs the soil and vegetation, and creates conditions favorable to
weed invasion.
Military use of the prairies varies over time according to the training needs of the U.S. Army, but can be
generalized in the following four categories: 1) impacts from projectiles, 2) vehicle maneuvers, 3) foot
traffic, and 4) excavation (Altman 2003). These activities typically result in damage to soil, vegetation,
and wildlife through soil compaction and contamination, release of toxic chemicals, noise disturbance to
wildlife, habitat loss and degradation, and introduction and spread of invasive weed seeds on transport
and other training equipment (Altman 2003). A potentially positive effect of military training on
butterfly habitat is the initiation of wildfires resulting from exploding munitions, especially on the
Artillery Impact Area.
Active management by Fort Lewis personnel and partners to enhance the condition of the prairies has
been in effect for several years. Management activities include area-specific rehabilitation efforts and
projects that target rare species. Invasive species control is widely practiced on the prairies with the aid
21
of mowers and herbicides. Prescribed fire is currently used as a management tool to enhance habitat
and reduce fuel loads on prairies and their edges.
Research Natural Areas and Seibert staked areas afford protection to prairies by limiting activities in
high quality habitats. Specific areas of select prairies are delineated by Seibert stakes that signal
restricted access. No vehicles, bivouacs or digging activities are permitted inside the staked area. These
areas are used primarily for protection of special status species, high quality sites, rehabilitation efforts,
or cultural sites.
The above uses contribute to both the degradation and enhancement / protection of butterfly habitat.
Current uses that complement enhancement efforts are encouraged (special protection status to limit
access by vehicles and horses, invasive species control), while those known to degrade habitat are
discouraged (destructive recreational and military uses) in areas targeted for habitat enhancement
activities on the high and secondary priority prairies. It may also be useful to include a brief
introduction to prairie conservation in training courses for Fort Lewis personnel.
5.3 How ? – Enhancement Techniques
Management actions recommended in this plan emphasize the enhancement of native prairie and
prairie-woodland ecotone features through the control of invasive species and subsequent planting of
native grasses and forbs in a variety of microhabitats. Strategies for controlling invasive species, and
seeding or planting of native species are complex subjects and generally rest outside of the intent for
this document. Some aspects of these restoration strategies are treated below by way of cursory
overviews of considerations that are important to butterflies and their habitat, and some of the gaps in
our knowledge of these strategies. Where possible, restoration strategies should be implemented in a
way that facilitates learning opportunities through careful research to allow application of lessons
learned in future restoration efforts. Specific considerations for rendering some enhancement
techniques (fire, mowing, herbicides) safer for butterflies are provided in section 7.1.
5.3.1 Controlling Woody Invasives
Efforts to reduce the threat of Scotch broom have been underway for several years on Puget praireis,
and have met with considerable success in reducing the cover and height of this woody invasive. Scotch
broom is difficult to eliminate, however, and thus maintenance efforts are ongoing to control the regrowth, re-establishment, and spread of this species. Control efforts incorporate a variety of tools,
including fire, mowing, brush-cutting, hand-pulling, and herbicides. Considerable attention has been
devoted to this problem area (Dunn 2003), and thus will not be elaborated in this plan, other than to
emphasize butterfly-sensitive considerations for use of these tools reviewed in section 7.1. Other woody
shrubs that require periodic control on the prairies or prairie ecotones include the non-native Himalayan
blackberry (Rubus discolor), and the native snowberry (Symphoricarpos albus).
It is also important to arrest or reverse the encroachment of Douglas-fir saplings and trees on the
prairies. Occasional trees or tree islands contribute to habitat diversity, but where Douglas-fir overtop
oaks, or contribute to a substantial reduction in prairie habitat, conifer saplings and trees should be
removed. The use of hand-held brush cutters, chain saws, or fire could be useful in controlling the
invasion of conifers on the prairie.
5.3.2 Controlling Herbaceous Invasives
Non-native forbs, especially hairy cat’s ear (Hypochaeris radicata), are very prevalent on the prairies,
although they do not appear to degrade the prairies to the extent that other woody and grass invasives
do. Furthermore, non-native forbs may provide important resources for butterflies. Taylor’s
22
checkerspots have used the non-native Plantago lanceolata as a larval food on the Puget prairies, and
non-native thistles, including Cirsium arvense, are important nectar resources for zerene fritillaries
(Hays et al. 2000). Control of non-native forbs will not be treated further in this plan, although the role
of non-native forbs in butterfly habitat constitutes a topic for future research (section 8).
Non-native grasses appear to be far more problematic than non-native forbs on the high priority prairies,
especially in relatively mesic sites and areas of the prairie that grade into riparian zones. In some of
these sites, tall aggressive pasture grasses dominate and have converted the once short-statured bunch
grass or sedge-dominated prairie vegetation to ‘hayfields’ of 1m+ tall grasses. Tall grasses that
dominate structural features of the prairies pose a considerable threat to butterfly habitat because they:
a) block access to native plants, and b) out-compete and eliminate native vegetation in these important
habitats, rendering them unusable to butterflies that rely on native resources. Shorter grasses such as
colonial bentgrass (Agrostis capillaris) also pose serious threats to butterfly habitat because they
compete for space with native species, and are widespread on some prairies, which limits control
options. A cursory review of control options for invasive grasses and their implications for butterfly
conservation is presented below.
Mowing
Annual spring mowing has the potential to reduce the vigor of some invasive grasses (Wilson and Clark,
2001), but the effects of mowing on Puget prairie grasses are unknown. Where species differ in height,
mowing may be a useful tool to target taller species, while not harming shorter species that are below
the cutting height. In the case of Puget prairies, mowing has the potential to be most effective at
controlling invasive grasses that are taller than the native fescue and danthonia (Danthonia californica),
such as tall oat grass (Arrhenatherum elatius), but would probably have little potential for controlling
shorter invasives such as colonial bentgrass, which is closer to the native fescue in height. Use of
mowing to control invasive grasses in a butterfly habitat improvement context would be controversial
because:
a) This strategy requires mowing in the spring, which could be lethal to some individual butterfly
larvae, pupae and adults, which are more likely to be active higher up on plant stems at that time
of year compared to their sedentary phase in the duff layer during the fall or winter.
b) Mowing is non-selective, and spring mowing could be detrimental to desirable native forb
butterfly resources, along with the target grasses.
The use of mowing as a tool to control invasive grasses may be useful in some sites, but less desirable in
the context of butterfly habitat enhancement where rare butterflies are present. The efficacy of mowing
to control invasive grasses is currently being investigated on Puget prairies by Scott Pearson of the
Department of Natural Resources.
Herbicides
The judicious use of grass-specific herbicides has the potential to considerably reduce the cover of nonnative grasses, while avoiding harmful impacts to the forb community. These herbicides are applied at
the critical growth stage when root resources have been depleted, and the grasses are translocating
resources (and the herbicide) to their roots, just prior to flowering (typically late April – early May).
One such herbicide, sethoxydim, kills grasses but has little or no impact on broadleaf herbs, woody
plants (Tu et al. 2001), or fine-leaved fescues. Whereas the native fescue and forbs may not be harmed
by these chemicals, other native grasses such as Koelaria cristata and Danthonia californica may be
affected (Robohm 1997), and it may be necessary to re-plant native grasses following herbicide
application on native plant communities. The chemical sethoxydim was used in a trial at the 13th
Division Prairie, where it killed colonial bentgrass within one week of application, while the fescue
remained unharmed (Robohm 1997). The bentgrass produced new growth at the site later that season,
however, and it is recommended that these herbicides be applied two times in a season, (e.g. spring and
after the fall rains) to be effective at killing pasture grasses with a well-established root network.
23
Grass-specific herbicides have the potential to control invasive grasses with fewer direct or indirect
impacts on native fauna and flora compared with mowing and prescribed grazing (see below). Over the
long term, herbicides may require fewer applications on the landscape compared with annual mowing,
with the result that the direct impacts of tractor movements on the prairies could be reduced through the
use of herbicides. The efficacy of herbicides to provide long-term (three or more years) control of nonnative grasses has not been empirically tested on Puget prairies, however, nor have the direct and
indirect impacts to the prairie vegetation and butterfly communities been comprehensively investigated.
The same is true of all the methods described here for invasive grass control in this section, and it would
be useful to proceed with a pilot program of herbicide application to address these information gaps.
Fire
Adaptation to fire by grasses is variable, and while some may respond to fire by decreasing, others can
increase (Robohm 1997, Grace et al. 2001). Grasses are best controlled if burned during their
vulnerable stage, and it is likely that repeat applications of fire would be most efficacious in controlling
non-native grasses (Tu et al 2001). Fire may be an important tool for the control of native grasses, but
its use should be pursued with the following cautions in mind.
Fire is likely to kill juvenile stages of butteflies, and thus needs to be used at a limited scale and at an
appropriate time (season). Fire has the potential to be maladaptive in the current context of invasive
plants due to the short-term increase in available N following the burn, and an increase in open sites for
invasive plant germination. Furthermore, fuel loads on some prairies and in their margins are high due
to the limited burning in recent history. High fuel loads may cause fires to burn at temperatures higher
than those to which the prairie community is adapted, and could be more detrimental to prairie flora and
fauna than helpful. In the case of high fuel loads, these sites could undergo fuel reduction through some
form of biomass removal, such as mowing or brush-cutting. As an alternative, the initial prescribed
burn could be implemented under moist or cool season site conditions, which should result in less
extreme heat.
Finally, implementation of a fire regime that includes annual burning is likely to be difficult to execute
on schedule due to the vagaries of the weather, coupled with regulatory restrictions (burn bans). In the
event that a prescribed fire is cancelled for the year due to unfavorable conditions or other reasons,
several other management activities may serve as short-term substitutes for fire. Mowing or applying
herbicide on woody shrubs or invasive grasses in the target area should serve to reduce the extent and
biomass of these pest species. In the case of mowing, it would probably be best to use a bagger to
remove the cut biomass from the site to remove a source of nitrogen to more closely mimic the
volatilization of nitrogen that would occur with fire. One option would be to conduct carefully
controlled ‘trash-can’ type contained burns on very small sections of the target area (e.g. patches of
violets) to influence the bare ground, moss, and thatch characteristics that would be difficult to affect
without the use of fire.
Grazing
Uncontrolled or excessive grazing is generally injurious to native habitats (Guppy and Shepard 2001).
The judicious use of grazing by cattle or sheep, however, has the potential to enhance butterfly habitat
by reducing the cover of invasive grasses, thereby favoring forb diversity and abundance. Cattle
grazing has been instrumental in the control of invasive grasses in California, with some benefits to
checkerspot populations (Weiss 1999), while historical grazing by sheep is believed to be instrumental
in the maintenance of habitat for Taylor’s checkerspot and zerene fritillary in British Columbia (Guppy
and Shepard 2001). Light grazing is proposed as a management recommendation for Taylor’s
checkerspot butterflies in Washington (Larsen et al. 1995), and therefore should be considered as a
potential tool for controlling invasive grasses.
24
Marty Chaney (pers. comm.) has observed that under well managed grazing regimes, cattle prefer to
graze the more succulent invasive grasses rather than the native fescue grass and forbs. Potter et al.
(1999), however, relate that cattle favor the native fescues as forage, and suggest that cattle grazing may
be detrimental to populations of mardon skippers.
Carefully managed grazing has the potential to control non-native grasses while benefiting the native
fescue and forbs. In this regard, it would be preferable to mowing as a tool to control invasive grasses
because of its selective nature. It also has the potential to reduce thatch depth, and hoof action may
break up the existing thatch layer. At the same time, cattle could have deleterious effects on the prairie
system such as increasing nitrogen through the deposition of urine and feces, and their hoof action could
compact soil and/or facilitate weed invasion by creating additional germination sites.
As with other techniques described above, grazing should be most injurious to the non-native grasses
during the spring growth phase, and then again in the fall after the rains initiate the fall flush of
vegetative growth. Spring is also the active phase of many of our Puget butterflies, and therefore
grazing has the potential to be harmful to individual butterflies during this season through trampling or
inadvertent consumption.
The logistics of managing cattle grazing on native prairies would be complex, labor intensive, and
costly. Cattle should be moved frequently using temporary electric fencing in the target zone to avoid
depleting the invasive grass forage and switching to native fescue and forbs. A disadvantage unique to
Fort Lewis is that the animals may ‘spook’ or otherwise react to the sounds of exploding munitions,
helicopters, or other training activities. The use of grazing as a habitat enhancement tool to control
invasive grasses would not be without controversy. In summary, the use of prescribed grazing, if
considered as a management tool, should proceed cautiously as a pilot project, and on a limited spatial
scale with a strong research component.
Summary
A multi-pronged approach, combining mowing, herbicides, and fire, may be necessary to reduce the
extent and vigor of non-native grasses on the prairies. Prescribed grazing using cattle also has the
potential to selectively target invasive grasses if managed correctly, but the logistics of this option may
preclude its application in a meaningful way. The use of any of these options should proceed cautiously
as pilot projects, and with strong research components that include collaboration or input from regional
scientists. In the interest of furthering butterfly conservation efforts as outlined in this plan, it may be
useful to institute some pilot projects to test combinations of mowing, herbicides and/or fire on the most
heavily degraded areas of 13th Division Prairie, and to a lesser extent, the western arm of Johnson
Prairie. Despite the cautions and concerns raised, aggressive control actions are warranted
because the full range of enhancement strategies in this plan cannot be accomplished without
control of invasive grasses in the more heavily invaded structural features such as relatively mesic
and edge habitats.
5.3.3 Planting Native Species
Direct seeding and transplanting ‘plugs’ of native grasses and forbs are techniques that have been used
for restoring patches of native species on Puget prairies (Dunn 1998). Seeds typically require the
presence of a disturbance mechanism to create bare soil for successful establishment, whereas nursery
plugs facilitate the survival and vigor of transplants into existing vegetation. Transplanting nursery
grown plugs into holes created with the use of a dibble planting bar, although more costly and labor
intensive than direct seeding, is the preferred method for establishing or augmenting specific resources
in existing prairie while avoiding large scale soil disturbance. Many species (eg. Erigeron speciousus)
exhibit better survival when planted out from a larger container than nursery plugs (Dave Hays, pers.
comm.), although the effort to grow and outplant larger individuals will require considerably more
25
monetary and labor resources than those required for plugs. Where safety concerns dictate that subsurface soil not be disturbed due to the possible presence of unexploded munitions, as on the Artillery
Impact Area, direct seeding without disturbance is recommended to augment native species populations.
Where native vegetation is relatively abundant, specific butterfly plant resources may be transplanted
into existing native vegetation to enhance the site’s potential as butterfly habitat. In potentially
important structurally diverse habitat sites, such as tree edges, prairie pockets, and relatively mesic areas
where invasives often predominate, strong measures to remove or control the invasives are warranted,
followed by the establishment of diverse suites of native plants emphasizing important butterfly
resources. Outplantings are likely to require considerable follow up ‘maintenance’ to reduce
competition from non-native grasses and forbs to ensure long-term survival and establishment (Dave
Hays, pers. comm.). Seeds for direct seeding and transplanting should be derived from Fort Lewis
prairie sources where possible to assure that plants are adapted to local conditions.
Site Preparation
Enrichment plants should not be transplanted into areas that are dominated by invasive species. Some
of the habitat enhancement patches identified for improvements in this plan (section 7) contain
structural features that are potentially important to butterflies, but are dominated by invasives. In these
enhancement patches, site preparation should consist of controlling invasive species and their seed
banks, if possible. Alverson’s (2002) observations from upland prairie restoration efforts in the
Willamette Valley of Oregon led to this opinion that “site conditions (i.e. the more complete removal of
weed seed) are a more important factor in native plant establishment than the quantity of seed that is
applied”. This opinion applies to direct seeding, but might also be considered relevant for transplanting
plugs into existing prairie dominated by weedy species. Planting trials of fescue plugs in degraded
Puget prairies invaded by colonial bentgrass revealed that the combination of applying a grass-specific
herbicide and a layer of mulch around the plugs to control competition from invasives had significant
positive effects on the growth of the fescue plugs (Robohm 1997).
In highly degraded but potentially important butterfly microhabitats, where invasives form the dominant
cover type and threaten to outcompete the transplants (eg. where prairie grades into the riparian zone on
13th Division Prairie RNA), drastic measures may be warranted to effect the removal of the entire
herbaceous layer along with its weed seed bank. One method to consider is solarization, a site
preparation technique that captures radiant heat energy from the sun to kill weeds and weed seeds
located under clear plastic sheeting. This energy causes physical, chemical, and biological changes in
the soil. These changes lead to reductions of soilborne plant pathogens such as fungi, bacteria, and
nematodes, along with any vegetation and seeds present. This site preparation technique requires large
quantities of plastic, which is costly and not environmentally friendly when disposed of, and would only
be suitable for sites dominated by non-native vegetation and lacking native species. Solarization might
be most effective in preparing a weed and weed seed- free site if used in conjunction with a spring
application of herbicide to kill much of the existing vegetation first (Alverson 2003). A combination of
techniques including herbicides, tilling, and solarization offers potential for establishing a community of
native plants with low levels of invasives (Alverson 2003).
In summary, site preparation (and maintenance) to promote survivorship and vigor of outplantings is
critical to the success of habitat enhancements for butterflies. The plantings recommended in this plan
often include suites of species to be distributed across varying habitat conditions, and pose a
considerable challenge for implementers of the plan to prepare sites that are relatively free of
competition for the transplants. The identification of site preparation techniques suitable for a range of
conditions will likely require considerable attention to research trials, combined with long-term
monitoring.
26
Planting Amendments
Idaho fescue is highly amenable to transplantation, and requires no additional amendments (Dunn
1998). First year results of an outplanting trial for Viola adunca indicate that this praire forb exhibits
high first year survival. First year results of a Castilleja hispida trial on Fort Lewis suggest that these
plants benefited from the addition of fertilizer, and thus 2.5 ml (0.5 tspn) of a 19:6:12 slow release
fertilizer is recommended for addition in the dibble hole at the time of planting (Grosboll and Fimbel
2003). Addition of fertilizer should be localized to the transplanted plug to avoid general fertilization of
the prairie vegetation, particularly invasive species, which are adapted to compete well for nutrients.
The secondary effects of planting amendments in general, and fertilizer in particular, on invasive plants
can reduce the overall effectiveness of the amendments for the target species (Dunn 1998), unless
applied very carefully. As a general rule, planting amendments are not recommended.
Planting Strategy
Habitat enhancement patches (described in section 5.1.2) are too large to receive 100% coverage of
plantings. Instead, one, or a combination of, the three planting strategies described below should
provide concentrations of butterfly resources (butterfly resource patches) within the habitat
enhancement patches (Figure 5.1). First priority for a planting strategy is to identify existing resource
patches for a particular butterfly, and then plant seeds or nursery plant plugs within 50 m of those
existing resource patches. This will require mapping existing larval and important nectar resources of
the four butterfly species (see section 7.1 for a listing of some of these resources) for each of the high
priority prairies.
Figure 5.1 Schematic showing hypothetical prairie with three habitat enhancement patches (A, B, anc C). The
proposed planting strategy emphasizes initially planting butterfly resource patches (eg. butterfly enrichment plots,
described below) within 50 m of a natural existing resource patch, and then expanding outward.
27
To avoid disturbance to butterflies and their existing resources, avoid planting where resources already
exist. Eventually, the aim is for butterfly resource patches (natural, or planted using one or more of the
three planting strategies below) to expand beyond the initial habitat enhancement patches to create a
more widespread coverage such that the larger habitat enhancement patches are separated by < 100 m
(Ann Potter, pers. comm.).
It will be important to monitor the general survivorship of outplantings to determine if they are
available to butterflies (section 8, question 1). Many of the plants may not survive in the short or longterm. Quantities of plantings proposed in this document assume mortality rates of < 25%. Transplanted
Roemer’s fescue plugs are likely to exhibit relatively low mortality and are not expected to require
substantial re-plantings. Some forbs, however, are likely to exhibit high rates of mortality within the
first few years, and will probably exceed the 25% mortality assumption. In these cases where mortality
exceeds 25%, dead plants will need to be replaced. Plantings are also likely to require substantial
maintenance efforts to promote suitable conditions for long-term survival of transplants. Monitoring
and research (section 8) will be an important component of a successful planting program to identify
suitable site preparation, planting, and maintenance methods and techniques for a variety of plant
species in a variety of site conditions.
Three Planting Strategies
1. Where native vegetation is relatively abundant, one or more plant species may be seeded or planted
to augment specific resources for butterfly species targeted in that habitat enhancement patch.
2. Where native vegetation is relatively abundant, but generally lacking in butterfly plant resources, a
‘butterfly enrichment plot’ targeting a specific butterfly species may be planted (Table 5.3).
Butterfly enrichment plots emphasize concentration of larval resources and some adult resources for
specific butterflies in approximately 8 m radius circles (200 m2). The circle shape was chosen to
minimize edge effects and consequently the potential for dispersal by butterflies outside of the
resource patch. A circular plot is also easy to install with a single stake and a string. Butterfly
enrichment plots should be located in the habitat to take advantage of naturally occurring structural
features such as swales and tree/woodland edges. In the event that a site does not accommodate an
approximate circle shape, the larval resources should be distributed in a clumped fashion
appropriate to the shape of the site. These butterfly enrichment plots constitute the primary means
of improving quantities of resource plants for butterflies.
28
Table 5.3 Species for planting in ~8 m radius (200 m2) ‘butterfly enrichment plots’ to target a specific butterfly
species. Viola adunca v. adunca plantings for mardon skipper and zerene fritillary to be concentrated in center
~16 m2 of plot (2.25 m radius or 4m x 4m square) to yield 12.5 plants/m2 for mardon skipper and 25 plants/m2 for
zerene fritillary. Species listed are local to Fort Lewis (LCTA 2003).
Butterfly
Enrichment Plantings
Management Considerations
Taylor’s
300 Castilleja hispida ssp. Hispida (larval host)
checkerspot
300 Camassia quamash v. azurea
100 Lomatium utriculatum
50 Lomatium triternatum v. triternatum
100 Fragaria virginiana ssp. Platypetala
50 Balsamorhiza deltoidea
Mardon
* Festuca roemeri (laval host)
• Fescue to be interspersed with bare
skipper
200 Viola adunca v. adunca
ground (bare ground cover at 10 – 20%)
(plant in center 2.25 m radius)
• Maintain low vegetation height (~ height
50 Lomatium utriculatum
of fescue and violets)
200 Camassia quamash v. azurea
50 Ranunculus occidentalis v. occidentalis
Zerene
400 Viola adunca v. adunca (larval host)
• Low thatch depth (2.25 – 3.5 cm)
fritillary
(plant in center 2.25 m radius)
• Low vegetation height (< 30 cm)
200 Sericocarpus rigidus
50 Erigeron speciosus v. speciousus
(plant distant from violets)
50 Solidago missouriensis v. tolmieana
(plant distant from violets to maintain
low vegetation height)
Puget blue
200 Lupinus albicaulis v. albicaulis (larval host)
200 Eriophyllum lanatum v. achillaeoides
100 Potentilla gracilis v. gracilis
* = As needed to bring cover value to 30% - 60%.
3. Where native vegetation is sparse, and invasive vegetation has been controlled, ‘basic prairie
planting blocks’ or ‘edge planting blocks’, incorporating suites of butterfly resources and relatively
common native prairie plants, are recommended to aid in the restoration of a more complex and
healthy community of native prairie vegetation. These blocks are 5m x 5m, and consist of suites of
plants (Tables 5.4 and 5.5) in a systematic planting array (Figure 5.2). These planting blocks would
be most applicable in the case of a site recently cleared of dominating shrubs or trees, and/or heavily
burned areas where there are opportunities for restoring a more complete native prairie community.
These planting blocks are relatively small in size (25 m2) and are to be used as ‘building blocks’ that
contribute toward the restoration of native prairie, while allowing for the interspersion of single
resource plantings or butterfly enrichment plots among the planting blocks to emphasize
enhancement of the site for specific butterfly species.
Although plant resources are normally clumped and irregularly spaced in the landscape, a
systematic planting strategy is recommended for the basic prairie and edge planting blocks. The
planting strategy described below incorporates planting blocks and centers as artificial constructs to
facilitate the planning and distribution of the plants during the planting process, and also to facilitate
the future location and monitoring of the success of the restoration plantings. This planting strategy
includes regular spacing of fescue (two fescue spacings, 0.5 m and 0.33 m, are recommended to test
the efficiency of meeting the habitat enhancement objectives, section 6), with clumpings of native
forbs and other graminoids in the interstitial spaces among the fescue. The primary caveat for this
planting protocol, however, is that when outplanting in the future, plants should be distributed in the
landscape in a manner consistent with their natural distribution, wherever known or possible.
29
Species recommended for use in the planting blocks are listed in tables 5.4 and 5.5. Forbs are
categorized as high, medium, and low density targets to reflect their relative abundance in the
planting mix based on their importance to butterflies and their relative abundance in native prairie
communities. High and medium density targets emphasize important butterfly resources and those
plant species that are most common on the prairies (Chappel and Crawford 1997), whereas low
density targets are species that are still commonly found on Puget prairies, but not known to be used
by butterflies. Specialty plants are relatively large and shrub-like, or typically require special site
considerations.
Basic Prairie Planting Block
Purpose: baseline planting block suited to open prairie site where native vegetation is sparse and
invasive vegetation has been controlled, to restore elements of native prairie vegetation
community with emphasis on butterfly resources (Table 5.4). The block is composed of
regularly spaced fescue plugs, with forb planting centers in the interstitial spaces among the
fescue. Forb planting centers may incorporate a single individual, or several individuals, of
a species.
• 5 m x 5 m block with one of two different spacings:
a) 121 fescue at 0.5 m spacing (Figure 5.2)
b) 256 fescue at 0.33 m spacing
• 50% fescue plugs : 50% forb and non-fescue graminoid plants
• composition of forb and non-fescue graminoid plants for interstitial spaces (planting centers):
a) 0.5 m fescue spacing - 8 planting centers for each high density species, 5 planting
centers for each medium density species and non-fescue graminoids, and 4 planting
centers for each low density species.
b) 0.33 m fescue spacing – 16 planting centers for each high density species, 11 planting
centers for each medium density species and non-fescue graminoids, and 8 planting
centers for each low density species.
• Four lupines (3 L. albicaulis, and 1 L. lepidus) and 4 Balsamorhiza deltoidea to be planted at
the exterior of each planting block because they have the potential to become large and shrubby,
and can dominate the local microsite.
• Spreading dogbane (Apocynum androsaemifolium) to be planted along road edges or sites with
little to no interspecific competition.
Edge Planting Block
Purpose: Same as baseline planting block above, except for use under and adjacent to oak trees, or
conifer trees or in relatively mesic conditions (Table 5.5). Graminoids are spaced at
regular intervals, with forb planting centers in the interstitial spaces among the graminoids.
• 5 m x 5 m block, with 0.5 m or 0.33 m graminoid spacing as above.
• (50%) graminoids : (50%) forbs
• composition of graminoids and forb to consist of:
a) 0.5 m spacing – 73 Carex inops, 24 Elymus glaucus, 16 Festuca roemeri, 8
Danthonia californica, and 20 planting centers for each high density forb species: 7
planting centers for each low density forb species.
b) 0.33 m spacing – 146 Carex inops, 50 Elymus glaucus, 40 Festuca roemeri, 20
Danthonia californica, and 40 planting centers for each high density forb species:
18 planting centers for each low density forb species.
Note: Plectritis congesta has been identified as an important larval food and adult nectar resource for
Taylor’s checkerspots at the Bald Hills site in western Washington. This annual also occurs on Fort
Lewis, but its distribution and abundance is very limited and has recently declined to just a few known
30
occurrences (LCTA 2003). This species is described as occurring in ‘vernally moist meadows and open
rocky slopes and bluffs’ (Pojar and MacKinnon 1994). These habitats are not prevalent on our lowland
Puget prairies, and therefore, this species may not be a robust candidate for augmentation on Fort Lewis.
It is worth investigating, however, conditions that would favor the establishment of this species, given
its potential importance to Taylor’s checkerspot butterflies. This species is not currently included on
the list of enhancement plantings due to a lack of local seed source and knowledge of site requirements.
The potential and suitability of this species as a Taylor’s checkerspot resource on Fort Lewis is included
as a subject for future research (section 8).
31
Scientific name
Graminoids
Roemer’s fescue
Long-stolon sedge
California danthonia
Festuca roemeri
Carex inops ssp. Inop
Danthonia californica
100
93
79
45
2
2
L
Camassia quamash v. azurea
Eriophyllum lanatum v. achillaeoides
Viola adunca v. adunca
Castilleja hispida ssp. Hispida
Lomatium utriculatum
Lomatium triternatum v. triternatum
86
93
64
43
-
6
2
4
<1
-
N
Hieracium cynoglossoides
Sericocarpus rigidus
Fragaria virginiana ssp. Platypetala
Solidago missouriensis v. tolmieana
Ranunculus occidentalis v. occidentalis
Potentilla gracilis var. gracilis
Erigeron speciousus v. speciosus
86
71
64
64
64
57
-
4
4
4
2
2
2
-
Microseris laciniata ssp. Laciniata
Dodecatheon hendersonii ssp. Hendersonii
Campanula rotundifolia
Koeleria macrantha
Prunella vulgaris ssp. Lanceolata
Achillea millefollium v. occidentalis
71
50
29
29
64
64
<1
<1
<1
2
<1
<1
Lupinus lepidus
Lupinus albicaulis v. albicaulis
Balsamorhiza deltoidea
Apocynum androsaemilfolium
64
21
-
2
3
-
Forbs
High density targets
Common camas
Oregon sunshine/woolly sunflower
Early blue violet
Harsh paintbrush
Spring gold
Nine-leaved lomatium
Medium density targets
Houndstongue hawkweed
White-top aster
Broadpetal strawberry
Missouri goldenrod
Western buttercup
Slender cinquefoil
Showy fleabane
Low density targets
Cutleaf microseris
Henderson’s shooting star
Bluebells of Scotland
Prairie junegrass
Selfheal
Yarrow
Specialty plants
Prairie lupine
Sickle-keeled lupine
Puget balsamroot
Spreading dogbane
32
Puget Blue
Zerene Fritillary
Common name
Taylor's
Checkerspot
Mardon Skipper
Constancy
% Cover
Table 5.4. Prairie plant species for use in ‘basic prairie planting blocks’(described above) by density target
categories. Species listed are local to Fort Lewis (LCTA 2003). Category designation based on: a) the species’
importance to butterflies and b) abundance (constancy and cover, Chappell and Crawford 1997) in the native
landscape. Specialty plants include species to be planted outside of planting blocks. L = larval host, N = nectar
resource.
N
N
N
N
N
L
L
N
N
N
N?
N
N
N
N
N
N
N
N
N
N
N
LN
N
N
Table 5.5. Plant species for use in ‘edge planting blocks’ (described above) at tree-prairie ecotones or relatively
mesic sites. Species listed are local to Fort Lewis (LCTA 2003). Constancy and cover values from nativedominated herbaceous vegetation plots in the Oregon white oak/long stolon sedge-camas community (Chappell
and Crawford 1997).
Common name
Scientific name
Constancy % Cover
Graminoids
Long-stolon sedge
Blue wildrye
Roemer’s fescue
California danthonia
Carex inops ssp. Inop
Elymus glaucus ssp. Glaucus
Festuca roemeri
Danthonia californica
Forbs
high density
Common camas
Early blue violet
Camassia quamash v. azurea
Viola adunca v. adunca
Oregon sunshine/woolly sunflower Eriophyllum lanatum v. achillaeoides
Spring gold
Lomatium utriculatum
Harsh paintbrush
Castilleja hispida ssp. Hispida
(observed under oaks at Bald Hill)
low density
Yarrow
Achillea millefollium v. occidentalis
Western buttercup
Ranunculus occidentalis v. occidentalis
Showy fleabane
Erigeron speciousus v. speciosus
(late season nectar source)
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
O
X
100
60
60
50
22
13
6
3
60
70
20
20
-
5
<1
6
4
-
70
60
-
4
2
-
Figure 5.2 A portion of a basic prairie planting block, 5 m x 5 m (0.0025 ha) showing partial array of 11 x 11 =
121 planting centers. Fescue (X’s) to be planted at 0.5 m or 0.33 m spacing, with forbs or non-fescue graminoid
(O’s) in interstitial spaces.
33
6. Habitat Enhancement Objectives
To satisfy the goal of enhancing habitat for four rare butterfly species on Fort Lewis, objectives were
developed to guide:
1. An overarching strategy for the Fort Lewis landscape as a whole,
2. enhancement actions at the prairie level, and
3. species’ level objectives for each of the four butterflies targeted in this plan.
These objectives are based on the best available ecological data presented in earlier sections of this
document, and are derived largely from the study of local populations by Hays et al. (2000).
Landscape Objective
Three high priority prairies meet prairie level objectives outlined below (see section 5.1.1 for
further background).
Prairie Objectives
1) For each high priority prairie, > 3 habitat enhancement patches (> 2 ha in size each) meet the
following high quality vegetation composition targets for the butterfly community, synthesized from
Hays et al. (2000) and Dorner (1999) (see Table 5.2 and section 5.1.2 for further background):
• Scotch broom
< 6% cover, and < 0.26 m in height
• Native grasses, dominated by fescue
30% - 60% cover
• Native forbs
> 25% cover
• Non-native grasses and forbs
< 35% cover
2) At least half of the habitat enhancement patches include diverse structural features other than
flat open prairie habitat.
Butterfly Objectives
For each of the four rare butterfly species, two prairies contain > 3 habitat enhancement patches
(> 2 ha in size each) per prairie, that meet species’ level objectives (elaborated below). For
example, objectives relating to the Taylor’s checkerspot include meeting criteria ‘a’ – ‘c’ below
in each of three or more habitat enhancement patches on each of two prairies highlighted in this
plan.
Taylor’s Checkerspot
a) Two larval resource species, Plantago lanceolata (non-native, do not plant) and
Castilleja hispida (> 200 plants) established and reproducing.
b) Three or more nectar resource species (Camassia quamash is the most important)
established and reproducing, especially:
− Camassia quamash
− Lomatium utriculatum
− Lomatium triternatum
− Fragaria virginiana
c) At least 2 habitat enhancement patches per prairie enhanced for Taylor’s checkerspot
incorporate diverse structural features (e.g. swales, relatively mesic areas, or tree edges)
other than flat open prairie.
Mardon Skipper
a) Abundant fescue (> 30% cover) interspersed with bare ground present at 10-20% cover.
b) Three or more nectar resource species established and reproducing, including
− Viola adunca (presence of clusters containing >11 plants/m2)
34
−
−
Vicia sativa (where present do not control, clusters extending 6 – 17 m in size)
Lomatium utriculatum (presence of clusters approximating 0.4 plants/m2 or
~0.7 m spacing)
c) At least 2 habitat enhancement patches per prairie enhanced for mardon skippers
incorporate diverse structural features (e.g. swales, mesic areas, or tree, trail, or road
edges) other than flat open prairie.
Zerene Fritillary
a) Abundant violets (Viola adunca clusters with >20 plants/m2) in habitat characterized by
− low thatch depth (2.25 – 3.5 cm), and
− low vegetation height (< 30 cm).
b) Two or more nectar resource species established and reproducing, especially:
− Erigeron speciosus
− Cirsium arvense (non-native, do not plant, do not control unless large patches
threaten landscape)
− Solidago missouriensis,
− Sericocarpus rigidus (syn: Aster curtus)
c) At least 2 habitat enhancement patches per prairie enhanced for zerene fritillaries
incorporate diverse structural features (e.g. swales, mesic areas, tree edges, or forest
nooks / pockets) other than flat open prairie.
Puget Blue
a) Abundant Lupinus albicaulis (density 0.1 – 2 plants/m2) for larval feeding and adult
nectaring.
b) Two or more additional nectar resource species (in addition to the lupines which also
serve as a nectar resource) established and reproducing, especially:
− Lomatium triternatum
− Eriophyllum lanatum
− Potentilla gracilis
− Vicia sativa (non-native, do not plant).
7. Prairie Enhancement Strategies
Strategies for enhancing butterfly habitat in each of the five prairies covered by this plan are presented
on the following pages. In some cases, details are offered to facilitate both the planning and
implementation phases of the enhancement work. Despite the level of detail, the reader should not
confuse precision for accuracy in determining the correct path to meaningful enhancements for prairie
butterflies. These strategies reflect application of the best available ecological information, and should
be considered more as guidelines than a recipe. Implementers of the plan will need to remain flexible in
the face of dynamic natural systems, and willing to incorporate new information, try new approaches,
and generally modify the proposed strategies to improve results as a response to quantitative and
qualitative research results and observations of progress made. Timely incorporation of results from
complementary research projects will facilitate the adaptive management process. Additionally, a
review of progress made in meeting the habitat enhancement objectives (section 6) in year three (end of
2006) would allow a formal opportunity for an assessment of the need to modify approaches
recommended in the plan.
Prairies are grouped as ‘high priority’ or ‘secondary priority’ (see section 5.1.1), although baseline
enhancement actions were developed for application on all prairies. Strategies for high priority prairies
35
emphasize greater enhancement efforts, including more aggressive invasive grass control and native
species plantings. Implementation of these enhancement actions should be conducted with special
provisions to minimize impacts to rare butterflies and their resources (considerations for ‘butterflysensitive’ management techniques are provided in section 7.1). Butterfly enhancements must be
conducted in a manner that promotes the continued existence of these rare butterflies where they
currently occur. Caution is warranted because isolated populations that are significantly reduced or
extirpated are not likely to re-establish naturally.
Several habitat enhancement patches in high priority prairies contain sites that are dominated by woody
and herbaceous invasives. Removal of invasives that dominate a site is the first step to enhancing these
areas. Specific planting recommendations for these sites should be developed after removal or control
of the invasives and examination of the condition of the underlying grass and forb layer. Enhancement
actions, especially those pertaining to control of invasives, should be considered more as maintenance
efforts to be repeated as needed, rather than single application management actions.
The exact location of plantings within a habitat enhancement patch is generally not specified in the
proposed strategies, but resources should generally be clumped to facilitate their use by butterflies. To
this end, a first approach would be to expand existing high quality resource patches. Secondarily, new
or enhanced resource patches should be established in close proximity (< 50 m) to the existing patches.
An additional consideration is that plants should be distributed among a variety of habitat types or
structural features, and in a manner that is consistent with the plant species’ ecology, where possible.
Finally, the number and type of plantings proposed for each of the high priority prairies (elaborated in
section 7.2 by prairie) were determined by an initial review of the quality and abundance of existing
vegetation and suitability for the butterfly species targeted. Proposed quantities are subject to revisions
based on future field observations of available resources and survivorship of enrichment plantings.
Baseline Recommendations Common to High and Secondary Priority Prairies
1. Maintain Scotch broom and woody invasives control across all high and secondary priority
prairies, while increasing efforts in the prairie-tree ecotones. It is important to continue to
control Scotch broom to avoid ‘losing ground’ on the progress made to date at keeping this
woody invasive at a manageable level. Activities to monitor and treat new invasives are
important to control non-native species before they become serious problems. Management
actions that target woody plant control should include considerations provided for
‘butterfly-sensitive’ strategies outlined in section 7.1 below.
2. Implement fire regimes as comprehensive ‘butterfly-sensitive’ fire plans that include
research components are developed for two high priority sites. In the interim, high and
secondary priority prairies could receive a program of limited prescribed burns that include
considerations for a ‘butterfly-sensitive’ fire strategy outlined in section 7.1 below.
3. Control conifer tree invasions into prairies and oak woodlands where applicable, through the
use of fire, cutting, and/or girdling of trees at prairie margins, and where warranted, the
central prairie area. Maintain some standing dead trees as snags for wildlife.
4. Consider as an emergency measure, watering important habitat patches (dense
concentrations of larval and/or nectar plant resources) under cases of extreme drought, for
the purpose of deferring senescence of important larval or nectar plant resources. This
emergency measure is justified on the basis that the fragmented and degraded prairies no
longer provide a ‘minimum dynamic area’ for many species that would seek out more mesic
habitats, and therefore active management such as emergency watering (perhaps with the
Forestry Department’s water tenders) may be warranted.
36
7.1 Considerations for Implementing Management Actions
Enhancements proposed in this plan represent an ambitious undertaking. The proposed plantings alone
could require a minimum of three years to implement, depending on availability of resources. As a
general rule, it would be prudent to implement enhancements slowly over a period of several years to
avoid impacting large areas of existing prairie at any one time. A period of approximately three years is
anticipated for the short-term implementation of proposed enhancements (section 9).
Implementation of enhancement activities should be most conservative on sites occupied by rare
species. This would include scheduling activities to avoid seasons of high vulnerability of the rare
butterflies and their important plant resources. As a general rule, it would be safest to implement
management activities in rare butterfly habitat that are likely to be harmful to active butterflies or their
resources, such as mowing or burning, during the quiescent stage of the butterfly life cycle (mid/late
September – mid April). Managers should strive to minimize combining multiple management actions
(i.e. mowing and fire) at a single site within an annual cycle. Combinations of management actions may
produce unpredictable synergistic effects on the butterflies or their habitat, and also confound
interpretation of research results.
In the interest of maintaining an active restoration crew year round, or if a management activity requires
implementation during larval feeding or adult flight periods, activities such as mowing could be
conducted in highly degraded sites or other areas where rare butterflies are not likely to occur (e.g.
monodominant stands of tall Scotch broom, or dense stands of invasive grasses). In this case, targeted
surveys could be conducted to confirm the absence of rare butterflies before implementation of the
management activity during the spring or summer active periods.
When management actions are required in rare butterfly habitat during feeding or flight periods, the
trade-offs in terms of costs and benefits to rare butterflies should be evaluated by managers in
consultation with butterfly ecology experts. If the management action is deemed to have a potentially
net positive effect for butterflies, considerations outlined below could be incorporated, along with
conducting the management action at a reduced scale of application, and incorporating a strong
monitoring and/or research component for the butterflies and their resources.
Similarly, if through annual monitoring, rare butterfly populations are observed to be declining, or are
determined to be especially low, biologists from the Washington Department of Fish and Wildlife
should be consulted to develop an appropriate course of action on habitat occupied by rare butterflies.
Finally, to reduce potentially harmful impacts on rare butterflies from management actions such as
burning, mowing, and application of herbicides, it is important to conduct these actions at an appropriate
scale that includes consideration of the distribution of adult and larval stages of the rare butterflies and
their plant resources. Specific considerations for implementing management actions in a ‘butterflysensitive’ manner were developed with input from Ann Potter (pers. comm.) and are included in the
strategies outlined below. Complementary research (section 8), including cost-benefit analylses, would
be useful to evaluate and refine these considerations through an adaptive management process.
Considerations for a ‘butterfly-sensitive’ fire strategy:
• Evaluate fuel loads present, and consider measures to control high fuel loads to avoid
generating extremely high temperatures.
• Map the distribution of: a) adult target butterflies (may include declining species beyond the
four rare species identified in this plan) and concentrations of their nectar plants or high use
areas and b) larval resources of target butterflies (i.e. map the actual distribution of adults, and
the potential distribution of larval stages of the target butterflies, see figure 7.1 for a
hypothetical example). Larval resources to map include:
37
Taylor’s checkerspot – Castilleja hispida plants within 100 m of another treated as one
resource patch. Plantago lanceolata plants within 100 m of another treated as
one resource patch (do not consider plants located in a trail or road setting).
Mardon skipper – dense, short stature fescue patches near patches of nectar resources
such as Viola adunca or Vicia sativa.
Puget blue – Lupinus albicaulis patches containing > 0.5 plants/m2, patches within 100
m of another treated as one resource patch.
Zerene fritillary - Viola adunca patches containing > 2 plants/m2 (most visible in May
and June), patches within 200 m of another treated as one resource patch.
•
•
•
•
•
In any single year, burn < ¼ of each ‘butterfly patch’ (adult use area and/or larval resource
patch), totalling approximately < ¼ of the prairie (yielding a burn interval of approximately 4 –
6 years).
Avoid burning during the flight season. Post larval diapause (dry- season) burning includes
August, September and October for mardon skipper, Taylor’s checkerspot and Puget blue
butterflies. Where zerene fritillaries may be present, avoid burning before September 20th.
Promote a shifting mosaic burn pattern to include irregularly shaped burn patterns harboring
unburned refugia within burn patches.
Include prairie – woodland/forest ecotones in the prescribed fire target area to enhance habitat
under and near trees.
Implement the burn in a way that facilitates learning opportunities through a strong research
component that includes replicates and controls (see section 8, question # 4, topic #4, for further
elaboration of research topics applicable to the use of fire). Incorporate annual monitoring of
butterflies and their resources to contribute to a better understanding of the impacts of fire (the
scale of monitoring will need to match the scale of the fire application to interpret meaningful
results concerning fire impacts). Pre-treatment monitoring data should be gathered prior to
implementation of prescribed burns to complement the post-treatment monitoring data.
Considerations for a ‘butterfly-sensitive’ mowing strategy:
• Map primary areas occupied or used by adult target butterflies (as above).
• Where rare butterflies are present, schedule mowing outside of the flight period: mow from late
July/August – late March for Taylor’s checkerspot, mardon skipper and Puget blue.
• Where zerene fritillaries are present, their flight period overlaps with the most effective time to
control Scotch broom. Therefore, if mowing during July/August/September in areas occupied
by zerene fritillaries, identify and delineate high use areas and nectar patches for zerene
fritillaries and mow < ¼ of each use area/nectar patch in a single year and during conditions that
allow escape flight (> 60o F, wind < 15 mph, enough sun to cast distinct shadows, and between
0900 – 1600 h).
• Include prairie – woodland/forest ecotones in the mowing target area to enhance habitat under
and near trees. Locate and flag oak and other native hardwood seedlings and saplings to alert
mowing personnel to their presence.
• Implement some mowing in a way that facilitates learning opportunities through a strong
research component that includes replicates and controls. Incorporate annual monitoring of
butterflies and their resources to contribute to a better understanding of the impacts of mowing
(the scale of monitoring will need to match the scale of the mowing application to interpret
meaningful results concerning mowing impacts). Pre-treatment monitoring data should be
gathered prior to mowing to complement the post-treatment monitoring data.
Considerations for a ‘butterfly-sensitive’ herbicide strategy:
• Map primary areas occupied or used by rare butterflies, and their resources, as described for fire
above.
38
•
•
•
•
•
In any single year, herbicide application not to exceed ¼ of each ‘butterfly patch’ (adult use
area and/or larval resource patch), totaling no more than ¼ of the prairie.
Apply herbicides outside of the flight period (Figure 2.1) in areas occupied by target butterflies.
The flight period of Taylor’s checkerspot overlaps with the most effective time to control
invasive grasses with herbicide. If an herbicide needs to be applied during the flight period of a
target butterfly, additional caution is warranted such that herbicide should only be applied
during conditions that allow escape flight (> 60o F, wind < 15 mph, enough sun to cast distinct
shadows, and between 0900 – 1600 h).
Include prairie – woodland/forest ecotones in the herbicide target area to enhance habitat under
and near trees.
The herbicide treatment should be implemented in a way that facilitates learning opportunities
through a strong research component that includes replicates and controls (see section 8 ,
question #4, topic #3, for further elaboration of research topics applicable to the use of
herbicides). Incorporate annual monitoring of butterflies and their resources to contribute to a
better understanding of the impacts of herbicides (the scale of monitoring will need to match the
scale of the herbicide application to interpret meaningful results concerning herbicide impacts).
Pre-treatment monitoring data should be gathered prior to the herbicide application to
complement the post-treatment monitoring data.
Finally, habitat enhancement actions should only be conducted at a time and place that is not in conflict
with military training activities.
Figure 7.1, An example of a prairie, for demonstration purposes, showing five hypothetical butterfly patches made
up of observations of adults, and/or larval and nectar plant resource patches (butterfly resource patches may be
naturally occurring or planted). Identified resource patches facilitate the planning process for prescribed burns
or other management actions having the potential to harm individual butterflies or their resources.
39
7.2 Prairie Specific Enhancement Strategies
High Priority Prairies
7.2.1 Artillery Impact Area
The opportunity to conduct management actions is very limited at this site because of its use as an
artillery practice range. Options for habitat enhancement are limited to activities in safe areas, and
activities that do not disturb subsurface soil due to the potential danger of unexploded munitions.
Known populations of rare butterflies occur primarily in the southwest portion (Taylor’s checkerspot
and mardon skipper), and along the southern boundary (mardon skipper) of the AIA. Exploration for
additional populations of butterflies or potential habitat has been very limited due to restricted access.
This prairie is extremely important because it is the only place on Fort Lewis that supports populations
of the federal candidate species: Taylor’s checkerspots and mardon skippers. These two populations are
highly vulnerable to stochastic events, as they appear to be small in number and restricted in space.
Therefore, considerable attention should be directed to this prairie in the future to determine the extent
of the distribution of existing populations of these and other rare species, along with a determination of
potential suitable habitat. The peripheral regions of the AIA are likely to provide some opportunities for
expanding, and/or enhancing butterfly habitat because the impact target range is primarily in the middle
of the AIA, leaving the periphery area relatively free of large artillery impacts, and also relatively free
of land training impacts. The periphery area is also subject to periodic burning, which may help to
promote some habitat characteristics that are favorable for butterflies. These same burns also pose a
potential risk factor, especially during the active phases of the two rare butterflies. Considerable
emphasis should be placed on expanding and enhancing habitat for Taylor’s checkerspot and mardon
skippers at the AIA.
Populations of Rare Butterflies
• Currently supports the only known population of the state and federal candidate species,
Taylor’s checkerspot, on Ft. Lewis. This population is also the only extant low elevation
population of Taylor’s checkerspot remaining in Washington.
• Currently supports the only known population of the state endangered and federal candidate
species, mardon skipper, on Ft. Lewis, which constitutes one of three extant populations in the
Puget Sound.
• Currently supports Puget blue butterflies.
Important Butterfly Habitat Considerations
• Military training activities (other than artillery practice) are limited at this site because of its use
as an artillery range.
• Supports a large population of Castilleja hispida, an important larval food plant for Taylor’s
checkerspot.
• Subject to occasional early season (spring and early summer) burns which may kill checkerspot
and skipper larvae, pupae, or adults, which are more active and potentially more vulnerable at
this time than other seasons (late summer or fall), and impact their larval and adult plant
resources.
• Subject to periodic burns, and therefore contains vegetation composition and structure
characteristics associated with frequent burning such as:
- abundant and diverse native forb community
- relatively low moss cover
- relatively abundant bare ground, creating open spaces among fescue and forbs to allow
butterflies access to oviposition sites and food plants
40
-
absence or low level of woody invasives (esp. Scotch broom)
low cover of tall non-native perennial pasture grasses that exclude native forbs and grasses.
Habitat Enhancement Activities (Figure 7.2)
Woody Invasives
Enhancement Patch A (outside of but adjacent to the AIA) – control Scotch broom in the
enhancement patch and surrounding greater triangle west of the road.
Non-native grass control
Control non-native grasses in enhancement patch A (directly adjacent to the AIA) - consider the
use of a grass-specific herbicide to avoid harm to native forb community and to prepare sites for
native plantings.
Plantings
First priority is to augment and expand existing resource patches (section 5.1.2). Secondarily,
new or enhanced resource patches should be established in close proximity (< 50 m) to the
existing resource patches. Some habitat enhancement patches have been identified for this
prairie (figure 7.2) based on the presence of native vegetation, structural features, and/or
location in the landscape.
Habitat Enhancement Patch A - directly adjacent (exterior to) the west side of the AIA. There is
some high quality vegetation here, and Puget blue butterflies have been observed at this
site. The current priority for this patch is the Puget blue butterfly, although this area
should be evaluated in the future regarding the potential for extending habitat for
Taylor’s checkerspot and mardon skipper, following on results of additional
investigations mentioned above.
− Plant 2 Puget blue ‘butterfly enrichment’ plots (this patch is outside of AIA boundaries)
Habitat Enhancement Patch B - large swale where mardon skippers observed historically.
Judging from nearby swale habitat in Patch C, the fescue and forb cover may be
limited.
− Make site visit to determine condition of swale and enhancement potential for mardon
skippers.
− If determined suitable for enhancement, direct seed Festuca roemeri and Viola adunca
v. adunca as appropriate as a minimum, and potentially Lomatium utriculatum and
Lomatium triternatum v. triternatum if forb component lacking. Add more seed in
succeeding years if germination is not successful.
Habitat Enhancement Patch C - supports generally high quality vegetation and supports the only
known population of Taylor’s checkerspot. Mardon skippers have been observed in the
swale in the south of this patch. The swale does not contain high quality vegetation,
and appears to be dominated by non-native low growing grasses (Aira sp.) and forbs
(Lotus sp.). Taylor’s checkerspot should be the priority for the northern and central
portion of this patch, while the mardon skipper should be the priority for the swale and
the generally southern portion.
− For Taylor’s checkerspot, expand the distribution of its important larval resource by
direct seeding Castilleja hispida ssp. Hispida (~ 100,000 seed [expect < 1%
germination] ) in two patches ~50m from current C. hispida populations. Add more
seed in succeeding years if germination is not successful. Evaluate timing of seeding in
relation to fire to achieve highest potential germination results (section 8, question #4,
topic #5).
41
−
For mardon skipper, direct seed Festuca roemeri, Viola adunca v. adunca, Lomatium
utriculatum and Lomatium triternatum v. triternatum in the swale in the southern
portion of the habitat patch where mardon skippers have been observed. Add more
seed in succeeding years if germination is not successful.
Other Actions
1. Explore options for expanding enhancement efforts beyond the boundaries of the habitat
enhancement patches outlined on the map, emphasizing edge areas along the south and east
of the Artillery Impact Area where mardon skippers were observed in the spring of 2003
(Morganweck and Dunn 2003).
2. Explore the need and options to minimize impacts of spring and summer burns on rare
butterflies and their resources by creating an intermittent fire-break to the north and west of
the current high use butterfly site (Enhancement Patch C). Options to consider might
include the following:
− Apply herbicide in a 3-5 m wide band ~100 – 200 m (allowing space for expanding
butterfly resources) outward from the exterior of the perimeter of the high use butterfly
zone (high quality prairie) to eliminate fire fuels, thereby slowing the advance of early
season burns.
− Maintain tree line break to the east and south of patch C and maintain berm to the east,
as these features are likely to be instrumental in protecting patch C from fires.
Figure 7.2 Artillery Impact Area on Fort Lewis showing outlines of proposed butterfly habitat
enhancement patches A, B, and C. Small case letters in italics indicate butterfly species targeted by
enhancements: m = mardon skipper, p = Puget blue, and t = Taylor’s checkerspot.
42
7.2.2 Johnson Prairie
Johnson Prairie is a relatively forb rich prairie distinguished by large swales. This prairie has a history
of supporting a diverse assemblage of butterflies, including rare species. Enhancements proposed below
should proceed slowly over several years to avoid impacting existing populations of zerene fritillaries
and Puget blue butterflies and their resources. The vegetation ranges from relatively tall and dense
concentrations of forbs and fescue, to relatively short stature open fescue dominated prairie. Short and
tall non-native grasses are prevalent, as are patches of Scotch broom. This would be a good site to test
the suitability of native thistles (Cirsium undulatum v. undulatum) as a zerene fritillary nectar source.
The combination of vegetation and structural features appears to be most suitable for the species
currently and formerly known to occupy this prairie, the Puget blue, zerene fritillary, and Taylor’s
checkerspot.
• Currently supports a Puget blue population.
• Currently supports a zerene fritillary population.
• Historically supported a Taylor’s checkerspot population.
Important Butterfly Considerations
• Highest documented abundance and diversity of butterflies compared to other Fort Lewis
prairies (Morgenweck and Dunn 2003).
• Supports a small population of Castilleja hispida
• Supports an abundant and diverse forb community.
• Includes diverse prairie structural features, including swales, oak woodlands, tree edges and tree
islands.
• The presence of pocket gophers (Thomomys mazama) has been documented on this prairie.
Woody Invasives
Control Scotch broom and invasive woody shrubs prairie-wide as needed, with special attention
to edge areas under oak woodlands and conifer edges. Enhancement patches containing high
quality native vegetation such as D and G (especially patch D which contains a population of
Castilleja hispida), or that support rare butterfly species such as patches A, B, and D, should be
considered for the use of low-impact or hand operated equipment that minimizes damage to
sensitive species. Large Scotch broom plants should be removed from the grasslands after
being cut where possible to reduce nitrogen and fuel levels. Remove encroaching Douglas-fir
seedlings, especially those that threaten to overtop oaks. Some (perhaps ~ 50%) of the large
Douglas-fir trees in enhancement patch A could be removed to control succession in this portion
of the prairie.
Non-native Grasses
Control non-native grasses in enhancement patches, especially A and D. Consider the use of a
grass-specific herbicide (see section 7.1) to avoid harm to native forb community and prepare
sites for native plantings.
Fire
Implement butterfly-sensitive fire regime upon completion of a plan. In the interim, adapt the
existing fire regime to incorporate considerations for a butterfly-sensitive fire regime, as
outlined in section 7.1.
43
Plantings
Habitat Enhancement Patch A – a small portion of prairie that is succeeding to conifer forest.
This area offers considerable protection from winds, and is generally open to the south,
promoting relatively warm conditions for the early spring butterfly, Taylor’s
checkerspot. At the same time, there is shade provided by conifer trees and topography
with northerly and easterly aspects in some areas, likely promoting some moisture
retention. Zerene fritillaries were observed in this patch in 2003, although nectar plants
were not in evidence. This area may be capable of supporting nectar resources
relatively late in the season due to portions having the potential for higher than average
moisture retention. This patch could be improved by removing some conifers, the
Scotch broom, controlling tall invasive grasses, and reducing the moss build up.
Enhancements in this patch target Taylor’s checkerspot and zerene fritillary.
− 10 edge planting blocks, (adjust number after evaluation of site condition following
removal of dense broom)
− forb component of 8 prairie planting blocks (fescue prevalent, but few forbs)
− 4 Taylor’s checkerspot enrichment plots (north-central and south central portions)
− 4 zerene fritillary enrichment plots (north-east and south-central portions)
Habitat Enhancement Patch B – bordered by conifers on three sides, with a generally southern
exposure. The site is currently dominated by Scotch broom and bracken fern, and is
frequented by zerene fritllaries, great spangled fritillaries, and Puget blue butterflies.
There is a patch of dogbane that was flowering during the zerene fritillary flight season
in 2003. Enhancements in this patch target Taylor’s checkerspot, zerene fritillary, and
the Puget blue butterfly (southern portion of the enhancement patch).
dense broom removal)
− 4 basic prairie planting blocks, (adjust number after evaluation of site condition
following dense broom removal)
− 2 Taylor’s checkerspot enrichment plots
− 2 zerene fritillary enrichment plots
− 2 Puget blue enrichment plot (southern portion of habitat enhancement patch)
− 100 Apocynum androsaemifolium.to expand the current patch along the roadway.
Habitat Enhancement Patch C – supports relatively short stature fescue-dominated vegetation
with relatively few forbs. The conifers to the west offer protection from some winds
and some afternoon shade. Enhancements in this patch target Taylor’s checkerspot,
zerene fritillary, and the Puget blue butterfly.
− forb component of 4 basic prairie planting blocks (fescue abundant, but few forbs)
− 2 zerene fritillary enrichment plots.
Habitat Enhancement Patch D – includes 2 swales and an open patch of conifer trees. Zerene
fritillaries use this site, and Erigeron speciousus was abundant during the 2003 flight
season, although violets were not evident. The vegetation on the west side of this patch
is relatively short and open, while the vegetation in the southeast tends to be tall and
44
forb rich. The west side of this patch may be suitable for Viola adunca establishment.
This patch also supports the main population of Castilleja hispida on Johnson Prairie,
and this population should be expanded. Enhancements in this patch target Taylor’s
checkerspot, zerene fritillary, and the Puget blue butterfly.
dense broom removal)
− 3 zerene fritillary enrichment plots, but may not need to plant Erigeron speciosus or
Sericocarpus rigidus, which are already abundant in this habitat patch.
− 2 Puget blue enrichment plot.
Habitat Enhancement Patch E – includes a low lying portion on both sides of the road in the
eastern portion of the habitat patch, which appears to retain more moisture than
surrounding prairie. The western portion is relatively short stature, open vegetation.
Enhancements in this patch target Taylor’s checkerspot, zerene fritillary, and the Puget
blue butterfly.
− 8 edge planting blocks (for relatively mesic conditions in eastern portion of patch)
− 2 Puget blue enrichment plot
Habitat Enhancement Patch F – includes a swale and some large trees. This habitat
enhancement patch supports some relatively short stature vegetation and limited forbs.
blue butterfly.
− 3 Puget blue enrichment plots
Habitat Enhancement Patch G - includes a swale in the southern portion and some large trees.
This habitat enhancement patch supports some relatively short stature vegetation in the
northern portion, and is forb rich (especially lupine) in the southern portion.
blue butterfly.
− 2 Puget blue enrichment plot.
Habitat Enhancement Patch H - includes a swale in the southern portion and some large trees.
This habitat enhancement patch contains abundant forbs. Enhancements in this patch
target Taylor’s checkerspot, zerene fritillary, and the Puget blue butterfly.
− 2 Taylor’s checkerspot enrichment plots, perhaps only Castilleja hispida necessary,
as nectar forbs may be abundant.
− 2 Puget blue enrichment plots (perhaps plant or promote dense concentration of
Lupinus albicaulis only, as nectar forbs were abundant in 2003).
Habitat Enhancement Patch I – edge habitat with extensions into forest matrix (‘Forest nooks’).
Formerly dominated by tall and dense concentrations of Scotch broom, recently mowed
in the fall, 2003. Enhancements in this patch target Taylor’s checkerspot, and zerene
fritillary butterflies.
45
−
−
−
8 edge planting blocks, (adjust number following evaluation where dense broom
removed)
2 Taylor’s checkerspot enrichment plots
2 zerene fritillary enrichment plots
Figure 7.3 Johnson Prairie on Fort Lewis showing outlines of proposed butterfly habitat enhancement
patches A through I. Small case letters in italics indicate species targeted by enhancements: p = Puget
blue, t = Taylor’s checkerspot, and z = zerene fritillary.
46
th
7.2.3 13 Division Prairie RNA
The 13th Division Prairie RNA and some associated prairie supports a combination of relatively short
stature open native vegetation, and relatively mesic sites dominated by dense stands of tall invasive
grasses that grade into riparian zones along the two creeks present. The combination of vegetation and
structural features appears to provide opportunities for enhancing habitat for all four rare butterfly
species.
• Currently supports a small Puget blue population.
• Recently supported a large Taylor’s checkerspot population.
• Historically supported zerene fritillaries.
• Includes Siebert staked and fenced areas that afford protection from many high impact training
activities.
• Supports natural and planted populations of Castilleja hispida.
• Supports high quality prairie areas with moderate forb densities.
• Includes diverse structural features including riparian corridors, deciduous and coniferous tree
edges and tree islands.
Woody Invasives
Control Scotch broom and woody shrubs prairie-wide as needed, with particular attention to
removal of woody shrubs at tree edges along South and Muck Creeks and under oaks in the
fenced areas of the triangle. Large Scotch broom plants should be removed from the grasslands
after being cut, where possible, to reduce nitrogen and fuel levels. Scotch broom mowing
occurred in August, 2003. Remove encroaching Douglas-fir seedlings, especially those that
threaten to overtop oaks.
Non-native Grasses
Control non-native grasses in enhancement patches - consider the use of a grass-specific
herbicide (see section 7.1) to avoid harm to native forb community and to prepare sites for
native plantings.
Special attention should be given to prairie - tree ecotones, especially under oaks in the triangle
area (enhancement patches D and E). The tall grasses in the relatively mesic sites adjacent to
the riparian zones along the two creeks in enhancement patches B, D, E, and F will require,
and warrant, aggressive control efforts.
Fire
Implement butterfly-sensitive fire regime upon completion of a plan. In the interim, adapt the
existing fire regime to incorporate considerations for a butterfly-sensitive fire regime, as
Plantings
47
Habitat Enhancement Patch A – just west of the airstip, this patch supports one of the largest
patches of Castilleja hispida on Fort Lewis. This patch is characterized by relatively
short stature, open vegetation incorporating a large population of forbs. The native
fescue is not abundant here. This patch also supports a population of the streaked
horned lark (Eremophila alpestris strigata), which also is of conservation concern.
Management actions for butterflies should be conducted in a manner consistent with
management recommendations for this streaked horned lark. Recommendations for
this species include avoiding disturbance (mowing, vehicle traffic, gatherings of people)
during the breeding season from early March until early August (Pearson 2003).
Pearson (2003) also recommends maintaining relatively short grasses and forbs (0 –
10”) and a relatively high percent (7 – 15%) of bare ground. Enhancements in this
patch target Taylor’s checkerspot butterflies.
− 5,000 fescue plugs (being careful to maintain bare ground specified above) as a
prairie base
− 2 Taylor’s checkerspot enrichment plots within 50 m of existing Castilleja hispida
(Lomatium spp. abundant at this site, not necessary to plant if still abundant)
Habitat Enhancement Patch B – includes relatively short stature open vegetation and relatively
mesic sites, the latter dominated by tall non-native grasses which require aggressive
measures for their control before plantings occur. Enhancements in this patch may be
distributed among the different site conditions to target Taylor’s checkerspot, mardon
skipper, zerene fritillary, and Puget blue butterflies.
− 15 edge planting blocks in relatively mesic zone grading into north riparian edge
− 4 mardon skipper enrichment plots
− 10 Quercus garryana (to increase hardwood tree structural diversity)
Habitat Enhancement Patch C – includes some topographical diversity and conifer tree islands
and forest edge. Currently supports scattered Erigeron speciousus. Vegetation is
variable due to variety of site conditions, although native forbs are generally not very
abundant. Enhancements in this patch may be distributed among the different site
conditions to target Taylor’s checkerspot, zerene fritillary, and Puget blue butterflies.
Habitat Enhancement Patch D – constitutes the western portion of the protected triangle area
between the confluence of Muck and South Creeks. This patch contains relatively short
stature open vegetation in the central northern portion. There is a row of oaks along the
northern boundary, and the understory contains an abundance of non-native grasses.
The southern portion of this patch grades into a riparian zone, and is dominated by tall
non-native grasses. The relatively mesic conditions in the southern portion could
provide longer lasting resources for butterflies if they could be converted to native
vegetation (in the relatively mesic areas that would support prairie forbs, not the wet
riparian zone). This southern area requires aggressive non-native grass control.
Enhancements in this patch may be distributed among the different site conditions to
target Taylor’s checkerspot, mardon skipper, and zerene fritillary butterflies.
− 10 edge planting blocks under the oaks
48
−
−
−
−
10 edge planting blocks in relatively mesic zone grading into southern riparian zone
3 Taylor’s checkerspot enrichment plots
3 mardon skipper enrichment plots
Habitat Enhancement Patch E - constitutes the eastern portion of the protected triangle area
between the confluence of Muck and South Creeks. This patch contains relatively short
stature open vegetation in the central northern portion. There is a row of oaks along the
northern boundary, and the understory contains an abundance of non-native grasses.
The southern portion of this patch grades into a riparian zone, and is dominated by tall
non-native grasses. The relatively mesic conditions in the southern portion could
provide longer lasting resources for butterflies if native vegetation (in the relatively
mesic areas that would support prairie forbs, not the wet riparian zone) were restored to
this area. This southern area requires aggressive non-native grass control.
Enhancements in this patch may be distributed among the different site conditions to
target Taylor’s checkerspot, mardon skipper, zerene fritillary, and Puget blue
butterflies.
− 15 edge planting blocks under the oaks
− 15 edge planting blocks in relatively mesic zone grading into southern riparian zone
− 10 Quercus garryana (to increase hardwood structural diversity)
Habitat Enhancement Patch F - contains relatively short stature, open vegetation in the central
southern portion, grading into tall non-native grasses as conditions become more mesic
near the riparian zone at the northern boundary. There is a row of hardwoods in the
riparian zone. The relatively mesic conditions in the northern portion could provide
longer lasting resources for butterflies if native vegetation (in the relatively mesic areas
that would support prairie forbs, not the wet riparian zone) were restored. This northern
area requires aggressive non-native grass control. Enhancements in this patch may be
distributed among the different site conditions to target Taylor’s checkerspot, mardon
skipper, zerene fritillary, and Puget blue butterflies.
− 10 edge planting blocks in the relatively mesic zone
Habitat Enhancement Patch G – has been logged and burned in recent history, providing
relatively favorable conditions for planting. This patch is generally level with large
conifers. Vegetation is relatively sparse, including a mix of native and non-native
grasses and forbs. Enhancements in this patch target Taylor’s checkerspot, mardon
skipper, and zerene fritillary butterflies.
− 20,000 fescue plugs
− 20 basic prairie planting blocks
− 10 edge planting blocks
49
−
Habitat Enhancement Patch H – is relatively level and featureless, but extends habitat westward
toward patch A primarily for Taylor’s checkerspot. Enhancements in this patch target
Taylor’s checkerspot, and zerene fritillary butterflies.
Habitat Enhancement Patch I – is relatively low-lying and mesic as it grades into the ripariain
zone on the northern portion of the patch. The relatively mesic area is dominated by
tall non-native grasses which should be removed before adding plantings.
Enhancements in this patch target Taylor’s checkerspot, and zerene fritillary
butterflies.
− 10 edge planting blocks for mesic area
Figure 7.4 13th Division Prairie RNA and associated ‘Pacemaker’ area showing outlines of proposed butterfly
habitat enhancement patches A, through I. Small case letters in italics indicate species targeted by
enhancements: m = mardon skipper, p = Puget blue, t = Taylor’s checkerspot, and z = zerene fritillary.
50
Secondary Priority Prairies
7.2.4 Weir Prairie Complex
The Weir prairie complex includes Upper, Lower, and South (south of Rainier Rd.) Weir Prairies.
These prairies have retained considerable coverage of fescue dominated vegetation, although the forb
populations and butterfly resources appear to be less abundant compared with the high priority prairies.
The Weir prairies also contain considerable populations of the introduced grass, Agrostis capillaris.
The combination of these three prairies offers the advantage of a large geographical area, taken together
with nearby Johnson Prairie, to provide the opportunity for a higher level meta-population, compared
with other prairies.
• Currently supports a zerene fritillary population
• Currently supports a Puget blue population
• Some protection from training activities afforded by Research Natural Area status.
• Supports high quality native prairie area with abundant fescue.
• Forbs present in moderate abundance on Upper Weir, but relatively limited on Lower and South
Weir.
• Includes some structural features such as coniferous and oak tree edges.
• South Weir constitutes the northern extension of a potential conservation area adjacent to Fort
Lewis.
Habitat Enhancement Activities
Control Scotch broom and invasive woody shrubs prairie wide as needed, with special attention to edge
areas under oak woodlands and conifer edges. Remove large Scotch broom plants from the prairie
where possible following cutting, as they may increase local nitrogen and fuel levels. Remove
encroaching Douglas-fir seedlings, especially those that threaten to overtop oaks. Monitor and treat new
invasive species. Adapt the existing fire regime to incorporate considerations for a butterfly sensitive
fire regime, as outlined in section 7.1.
7.2.5 Training Area 7S
This prairie has been severely impacted by the development of a gravel pit on the lower tier. There is an
upper tier of the prairie that continues to offer high quality vegetation, but this habitat is threatened by
future expansion of the gravel pit. This prairie is distinguished by the inclusion of a ponderosa pine
savanna and numerous structural features that offer a high level of structural diversity, despite the
relatively small size. Butterfly surveys in 2003 revealed for the first time, the absence of the historical
population of Puget blue butterflies that occupied this site.
• Formerly supported a Taylor’s checkerspot population.
• Status of Puget blue population uncertain – historically present, but not detected in 2003 survey.
• Includes a Siebert staked area that affords protection from many high impact training activities.
• Supports a population of Castilleja hispida, an important larval food plant for Taylor’s checkerspot.
• Supports a high quality prairie area with abundant forbs.
51
•
•
•
Includes diverse prairie structural features including terraces, deciduous and coniferous tree edges
and tree islands.
Supports abundant Vicia sativa under the oaks, which could serve as a nectaring source for mardon
skippers.
Supports ponderosa Pine savanna, and mardon skippers are known to use this habitat type
elsewhere.
Habitat Enhancement Activities
Control Scotch broom and invasive woody shrubs prairie wide as needed, with special attention to edge
areas under oak woodlands and conifer edges. Large Scotch broom plants should be removed from the
grasslands where possible after being cut, to reduce nitrogen and fuel levels. Remove encroaching
Douglas-fir seedlings, especially those that threaten to overtop oaks. Monitor and treat new invasive
species. Adapt existing fire regime to incorporate considerations for a butterfly-sensitive fire regime, as
8. Research and Monitoring to Guide Enhancement Actions
It is important to implement monitoring and research activities in conjunction with the enhancement
activities to address several questions that could lead to improvements in habitat management for rare
butterflies. These questions are addressed below.
Question #1. Are the prairie enhancement strategies suitable for meeting the habitat enhancement
objectives outlined in the plan?
Measuring the ultimate success of enhancement efforts to promote the long-term persistence of rare
butterflies is not possible at Fort Lewis at this time due to the limited occurrence of the rare butterfly
species there. It is possible, however, to monitor and evaluate the success of enhancement efforts in
meeting the habitat enhancement objectives recommended for Fort Lewis in this plan (section 6). In
addition, ‘off-site’ (outside of the Fort Lewis military complex) experimental approaches to
enhancement in habitat occupied by the rare butterflies would allow testing of effects of the
enhancements directly on the target butterflies themselves (see Question #2 below for further
development of this topic).
The success of habitat enhancement actions on Fort Lewis to achieve the habitat objectives outlined in
this plan may be evaluated through vegetation monitoring and sampling in enhanced areas. It is
important to track the survivorship of outplantings to determine if the resources are available to
butterflies. If mortality of transplants exceeds 25%, dead plants should be replaced. Other parameters
to consider measuring would be the percent cover by plant species or plant group, frequency or density
of plant species or plant groups, and other specific vegetation or site characteristics identified in the
objectives (section 6), including vegetation height, thatch depth, and amount of bare ground. These
measurements should commence in 2005 or 2006, to allow plants to establish and grow to a sufficient
size to be measured, and monitoring should continue for a minimum of five years to evaluate the longterm success (Dave Hays, pers. comm.).
Question #2. What is the response of the rare butterflies to habitat enhancements?
Fort Lewis
Opportunities for measuring the response of rare butterflies to habitat enhancements at Fort Lewis:
• Taylor’s checkerspot and mardon skipper responses to very limited enhancements on the
Artillery Impact Area (AIA).
52
•
•
Zerene fritillary responses to enhancements at Johnson Prairie.
Puget blue responses to enhancements at the AIA, Johnson Prairie, and the 13th Division Prairie
RNA.
In the areas outlined above, monitoring populations during their flight periods will provide
documentation of use in enhanced areas and population trends through time. These monitoring
activities could overlap with the rare species butterfly monitoring program discussed in question #3
below, so that rare species monitoring data may be used to address both questions #2 and #3, where the
technique yields detailed and comprehensive data.
On a finer scale, adult and/or larval use of resources (especially larval host and nectar plants) in the
enhanced habitat patches should be documented through direct observation, or indirectly through the use
of ‘sign’, such as larval feeding damage on host plant leaves. Investigations of this nature will be most
limited for the two highest conservation priority species, the Taylor’s checkerspot and mardon skipper
due to restrictions on habitat enhancements and limited access in the AIA. More comprehensive
assessments could eventually occur if mardon skippers and Taylor’s checkerspots are reintroduced to
the enhanced priority prairies in the future.
‘Off-Site’
In the interim, for the purpose of gaining information on the value of select enhancement actions
proposed in this plan, an off-site research program warrants consideration. Cooperating with scientific
partners on local non-military lands outside of the Fort Lewis complex, where the target butterfly
species occur, would allow investigation into topics that relate directly to the butterflies themselves (as
opposed to their habitat characteristics). For example, this approach would be especially useful in
investigating questions relating to the use of improved edge habitat, or the use of concentrated violet
plantings by mardon skippers at the Scatter Creek Wildlife Area.
Question # 3. What are the long-term population trends of rare butterflies in relation to the general
butterfly community on Fort Lewis?
It is important to monitor populations of rare butterfly species on Fort Lewis to track long term
population trends. At the same time, it is important to track changes in the general butterfly community
in the larger context of the Fort Lewis prairie complex through a broad-base, coarse-level butterfly
monitoring program. A program that emphasizes monitoring for rare species should be integrated with
the monitoring program for the greater community of butterflies on Fort Lewis. The topic of long-term
monitoring is raised in the context of this enhancement plan because it is important to track trends in
abundance of the rare butterflies, along with the butterfly community, to assess the long-term impacts of
enhancement or other management actions on all butterflies. This monitoring program could
complement the finer scale, directed research topics raised in question #2 above. A monitoring program
to address both rare species and the greater butterfly community is scheduled to be developed in the
future.
Question # 4. How can enhancement and management efforts be improved for rare butterflies?
Further research is needed to address the gaps in knowledge about the ecology of the rare butterflies,
their habitat requirements, and the proposed enhancement techniques. Several topics of inquiry are
identified below as important research subjects to guide current and future enhancement actions,
although this list is by no means exhaustive. Components of these research topics should be
incorporated into the implementation and evaluation of enhancement actions described in section 7.2 for
the high priority prairies where applicable.
53
Important Research Topics
1. Greater understanding of the distribution and habitat use by the four target species, especially
Taylor’s checkerspot and mardon skipper populations at the Artillery Impact Area and other ‘offsite’ Puget prairies. Some of the questions identified below represent an extension of the research
conducted by Hays et al. (2003), or were previously highlighted as topics for further research by the
authors.
Purpose – To guide enhancement actions for the four rare butterfly species at the AIA, Fort Lewis
and Puget region in general.
Approach - Research to investigate:
• Distribution, abundance, and use of different components of the habitat (nectar and larval
resources, structural features) by these species:
− on the AIA and surrounding habitat (especially the mardon skipper and Taylor’s
checkerspot)
− other Puget prairies
• The relationship between fire and Taylor’s checkerspot and mardon skippers at the Artillery
Impact Area, including the past history of the impact of fires on the butterflies and their
plant resources at the AIA. As an extension, explore the need for protection of critical
habitat from spring and early summer burns.
• Differential survival/mortality of eggs, larvae and pupae as a function of habitat type (open
prairie, conifer tree edge, deciduous tree edge, swale, riparian or mesic site, etc.) under
varying weather conditions.
• Population demographics of the rare butterflies.
• Determinants of dispersal and colonization abilities among habitat patches.
• Documentation of the phenologies of butterfly life cycles in relation to the phenologies of
their food and nectar plants in different habitats and different years.
• Vegetation composition and structure of high vs. low use sites (plant stature, densities,
spacing, bare ground, edaphic features, etc.).
• Nectar and larval host preferences in different years and sites, use vs. availability, and
response to enhancement measures and plantings.
• Feeding mechanisms of Puget blue butterflies on unopened L. albicaulis flowers.
• The relationship between Puget blue butterfly larvae and ants.
• Exploration of additional late season nectar resources, including native and non-native
forbs, especially thistles.
• Exploration of the role of non-native forbs as butterfly resources.
2. Investigation into planting techniques, including site preparation and planting amendments, and
control of invasives, that are most effective at promoting the establishment and maintenance of a
diverse native plant community.
Purpose – To guide planting and invasive species control protocols that are efficacious in
establishing and maintaining native plant communities with few invasive plants.
Approach – Research to investigate the most effective and efficient site preparation and planting
techniques in a variety of field conditions from existing native prairie to highly degraded prairie,
including applications of direct seeding and transplanting of nursery plugs to establish and maintain
diverse native communities while controlling invasive plants. Research to include replicated
designs within the context of Fort Lewis, as well as other Puget prairies.
3. Greater understanding of the role of grass-specific herbicides as prairie restoration tools to control
invasive grasses in butterfly enhancement sites.
Purpose – To guide restoration actions in enhancement sites where invasive pasture grasses
dominate.
54
Approaches – Investigate the application of a grass-specific herbicide at an enhancement site
containing a mixture of native and non-native vegetation (especially tall grasses and colonial
bentgrass), combined with a laboratory investigation to evaluate the effects on lepidopteran larvae.
Specific topics to investigate:
• Efficacy of a grass-specific herbicide in controlling the target invasive grasses in the shortterm (1 year) and long-term (3 years).
• Impacts of the herbicide on non-target vegetation (native grasses and forbs).
• Impacts of the herbicide on butterfly larvae (test on common butterfly or moth species
through collaboration with environmental toxicologist at Puyallup laboratory).
Field testing of a grass-specific herbicide would be especially useful at the 13th Division Prairie RNA
where there are extensive areas of habitat dominated by tall pasture grasses, and other areas with
considerable colonial bentgrass cover, as well as a mixture of native grasses and forbs. These mixed
conditions would allow investigation of the herbicide’s effects on both target and non-target species.
4. Greater understanding of the role of fire as a prairie process, and also as a restoration tool to
enhance butterfly habitat in the prairies and prairie edges.
Purpose – To guide the use of fire in prairie enhancement actions on Fort Lewis and other Puget
prairies.
Approach – Collaborate with fire ecology experts to design and execute long-term studies to
complement a ‘butterfly –sensitive’ fire plan (section 5.2.3 and 7.1 for characteristics to consider),
for the purpose of addressing the following topics:
• The optimum fire intensities, return intervals, and burning techniques to achieve the
following desired butterfly habitat characteristics:
− low moss cover and thatch depth
− presence of bare ground component of the prairies
- allows access to base of plants for oviposition,
- nesting sites for ground nesting invertebrates such as bees (eg bumblebees
pollinate Castilleja spp.)
- germination sites for plants (advantage and disadvantage at the same time)
− low woody shrub cover
− low invasive grass cover
− high forb abundance
− short-stature prairie vegetation
• The identification of non-native plants that increase and decrease with fire, and site and
burn conditions that may influence those responses.
• The effects of different burn/non-burn patch configurations and densities on floral and
faunal composition of burned prairies and the creation of burn refugia (e.g. multiple small
burns vs. patchiness within a single large burn… the SLOSS debate as applied to burn
refugia).
• Techniques to incorporate diverse habitat features such as prairie edges and mesic areas in
burn regimes.
• The use of burned areas compared with unburned areas, by butterflies.
• Mortality rates for butterflies as a direct or indirect result of fire.
5. Greater understanding of the natural ecology and germination and growth requirements of larval
resources for the rare butterflies: Festuca roemeri, Castilleja hispida ssp. Hispida, Plectritis
congesta, Viola adunca v. adunca, and Lupinus albicauli v. albicaulis.
Purpose – To guide enhancement actions that include management for these species as larval host
plants for rare butterflies.
Approach - Research to investigate:
• Population demographics
55
•
•
•
•
•
•
Response to fire (germination, growth, and survivorship)
Pollination
Hemiparasitism for Castilleja hispida ssp. Hispida
Senescence patterns in different microhabitats
Site requirements – potential for establishment along moisture and light gradients.
Site requirements, propagation, and seeding potential for establishing large patches of the
annual forb, Plectritis congesta, with subsequent determination of factors necessary to
maintain a substantial population, with an overall evaluation of its suitability as a Taylor’s
checkerspot resource.
6. Greater understanding of the wind, temperature, and moisture variables associated with prairie
structural features, including prairie ‘pockets’, prairie-tree edges, ‘swales’ and relatively mesic
areas, compared with open prairie sites.
Purpose – To guide enhancement actions that target improvements in prairie structure.
Approach – Collaborate with environmental science experts to design research to investigate:
wind, temperature, and moisture variables associated with open prairie habitat and
diverse structural features during post-diapause larval feeding and adult flight phases
(early spring through summer).
7. Greater understanding of the historical condition and processes of the Puget prairies in general, and
the prairies targeted for enhancement on Fort Lewis, in particular.
Purpose – To develop a model of historic conditions and processes in the local prairie landscape to
guide prairie restoration actions on Fort Lewis and the Puget region
Approach - Consult historical resources, including GLO land survey maps and survey notes to
describe historical vegetation conditions and site features, including the extent and configuration of
mesic sites, springs, or riparian zones where possible, while describing the extent and distribution of
vegetation types, including grassland, oak and/or ponderosa pine savanna, woodlands, and conifer
forest. Investigate the historical influence of Native Americans and wildlife on the process
component of the Puget prairies. Investigate the effects of soil N enrichment as a present day
process vs. historical context, on the invasion of native communities by non-native species.
9. Timeline
Short-term and long-term strategies are proposed for implementation of the enhancement activities.
Short-term strategy (2004 - 2006)
A short-term strategy includes the implementation of prairie specific enhancement and research
activities proposed for the three high priority prairies over a three year period, adapting and improving
enhancement objectives and activities as new information becomes available. Also for the short-term
could be the implementation of ‘butterfly-sensitive’ burning regimes with research components on two
prairies by the end of the short term (Figure 9.1).
Long-term strategy (2007+)
A longer-term strategy could incorporate a continuation and expansion of prairie enhancement and
research activities on the high priority prairies and at new sites. Other sites to be considered for further
butterfly habitat enhancement could include:
1. new habitat patches on the high priority prairies,
2. prairie habitat adjacent to the Artillery Impact Area, and
3. increasing efforts on the secondary priority Weir prairie complex and Training Area 7S, if
deemed appropriate at that time.
56
Activity
2004
2005
2006
spring summer fall winter spring summer fall winter spring summer
fall
seed collecting
planting
non-nat. grass control
butterfly monitor/res.
vegetation monitor/res
butterfly-sensitive fire*
* Incorporate considerations for a butterfly-sensitive fire regime provided in section 7.1 pending the
completion of a butterfly-sensitive fire plan.
Figure 9.1 Timeline of short-term activities for this enhancement plan.
Acknowledgements
This prairie enhancement plan was made possible by the generous sharing of time, ideas, and scientific
literature by the greater community of Puget prairie enthusiasts. I am grateful for the patience of the
following people who answered my endless questions, opened their libraries to me, or assisted in some
way with the development of this plan (alphabetical order).
Barry and Darlene Bidwell, Scott Hoffman Black, Marty Chaney, Chris Chappell, David Clouse, Eric
Delvin, Patrick Dunn, Peter Dunwiddie, John Fleckenstein, Jeff Foster, Rod Gilbert, Dan Grosboll, Bob
Hardwick, David Hays, Marion Jarisch, Angel Lombardi, Maija Morgenweck, Scott Pearson, Jonathon
Pelham, Debbie Pickering, Ann Potter (special mention for considerable assistance), Van Purdue,
Cheryl Schultz, Mace Vaughan, and Todd Zuchowski.
Despite the considerable input from these many people, I am responsible for any errors in the plan.
Personal Communications
Chaney, Marty. 2003. Natural Resource Conservation Service. Olympia, WA.
Hays, Dave. 2003. Washington Department of Fish and Wildlife, Olympia, WA
Pelham, Jonathon. 2003. Burke Museum, Tacoma, WA.
Potter, Ann. 2003. Washington Department of Fish and Wildlife, Olympia, WA.
57
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Habitat enhancement for rare butterflies on Fort Lewis prairies

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